Tamoxifen Citrate (tamoxifen citrate 10 mg) Dailymed

   

WARNING

For Women with Ductal Carcinoma in Situ (DCIS) and Women at High Risk for Breast Cancer

Serious and life threatening events associated with tamoxifen in the risk reduction setting (women at high risk for cancer and women with DCIS) include uterine malignancies, stroke and pulmonary embolism. Incidence rates for these events were estimated from the NSABP P-1 trial (see CLINICAL PHARMACOLOGY: Clinical Studies: Reduction in Breast Cancer Incidence in High Risk Women). Uterine malignancies consist of both endometrial adenocarcinoma (incidence rate per 1,000 women-years of 2.20 for tamoxifen vs. 0.71 for placebo) and uterine sarcoma (incidence rate per 1,000 women-years of 0.17 for tamoxifen vs. 0.4 for placebo)*. For stroke, the incidence rate per 1,000 women-years was 1.43 for tamoxifen vs. 1.00 for placebo**. For pulmonary embolism, the incidence rate per 1,000 women-years was 0.75 for tamoxifen vs. 0.25 for placebo**.

Some of the strokes, pulmonary emboli, and uterine malignancies were fatal.

Healthcare providers should discuss the potential benefits vs. the potential risks of these serious events with women at high risk of breast cancer and women with DCIS considering tamoxifen to reduce their risk of developing breast cancer.

The benefits of tamoxifen outweigh its risks in women already diagnosed with breast cancer.

*Updated long-term follow-up data (median length of follow-up is 6.9 years) from NSABP P-1 study. See WARNINGS: Effects on the Uterus: Endometrial Cancer and Uterine Sarcoma.

**See CLINICAL PHARMACOLOGY: Clinical Studies: Table 3.

Description

Tamoxifen Citrate Tablets USP, a nonsteroidal antiestrogen, are for oral administration. Tamoxifen citrate tablets are available as:

10 mg Tablets. Each tablet contains 15.2 mg of tamoxifen citrate which is equivalent to 10 mg of tamoxifen.

20 mg Tablets. Each tablet contains 30.4 mg of tamoxifen citrate which is equivalent to 20 mg of tamoxifen.

Each tablet contains the following inactive ingredients: anhydrous lactose, colloidal silicon dioxide, crospovidone, magnesium stearate, microcrystalline cellulose and sodium lauryl sulfate.

Chemically, tamoxifen is the trans-isomer of a triphenylethylene derivative. The chemical name is (Z)2-[4-(1,2-diphenyl-1-butenyl) phenoxy]-N, N-dimethylethanamine 2-hydroxy-1,2,3- propanetricarboxylate (1:1). The structural and molecular formulas are:

Tamoxifen citrate has a molecular weight of 563.62, the pKa' is 8.85, the equilibrium solubility in water at 37°C is 0.5 mg/mL and in 0.02 N HCl at 37°C, it is 0.2 mg/mL.

Clinical Pharmacology

Tamoxifen citrate is a nonsteroidal agent that has demonstrated potent antiestrogenic properties in animal test systems. The antiestrogenic effects may be related to its ability to compete with estrogen for binding sites in target tissues such as breast. Tamoxifen inhibits the induction of rat mammary carcinoma induced by dimethylbenzanthracene (DMBA) and causes the regression of already established DMBA-induced tumors. In this rat model, tamoxifen appears to exert its antitumor effects by binding the estrogen receptors.

In cytosols derived from human breast adenocarcinomas, tamoxifen competes with estradiol for estrogen receptor protein.

Absorption and Distribution

Following a single oral dose of 20 mg tamoxifen, an average peak plasma concentration of 40 ng/mL (range 35 to 45 ng/mL) occurred approximately 5 hours after dosing. The decline in plasma concentrations of tamoxifen is biphasic with a terminal elimination half-life of about 5 to 7 days. The average peak plasma concentration of N-desmethyl tamoxifen is 15 ng/mL (range 10 to 20 ng/mL). Chronic administration of 10 mg tamoxifen given twice daily for 3 months to patients results in average steady-state plasma concentrations of 120 ng/mL (range 67 to 183 ng/mL) for tamoxifen and 336 ng/mL (range 148 to 654 ng/mL) for N-desmethyl tamoxifen. The average steady-state plasma concentrations of tamoxifen and N-desmethyl tamoxifen after administration of 20 mg tamoxifen once daily for 3 months are 122 ng/mL (range 71 to 183 ng/mL) and 353 ng/mL (range 152 to 706 ng/mL), respectively. After initiation of therapy, steady-state concentrations for tamoxifen are achieved in about 4 weeks and steady-state concentrations for N-desmethyl tamoxifen are achieved in about 8 weeks, suggesting a half-life of approximately 14 days for this metabolite. In a steady-state, crossover study of 10 mg tamoxifen citrate tablets given twice a day vs. a 20 mg tamoxifen citrate tablet given once daily, the 20 mg tamoxifen citrate tablet was bioequivalent to the 10 mg tamoxifen citrate tablets.

Metabolism

Tamoxifen is extensively metabolized after oral administration. N-desmethyl tamoxifen is the major metabolite found in patients' plasma. The biological activity of N-desmethyl tamoxifen appears to be similar to that of tamoxifen. 4-Hydroxytamoxifen and a side chain primary alcohol derivative of tamoxifen have been identified as minor metabolites in plasma. Tamoxifen is a substrate of cytochrome P-450 3A, 2C9 and 2D6, and an inhibitor of P-glycoprotein.

Excretion

Studies in women receiving 20 mg of ¹⁴C tamoxifen have shown that approximately 65% of the administered dose was excreted from the body over a period of 2 weeks with fecal excretion as the primary route of elimination. The drug is excreted mainly as polar conjugates, with unchanged drug and unconjugated metabolites accounting for less than 30% of the total fecal radioactivity.

Special Populations

The effects of age, gender and race on the pharmacokinetics of tamoxifen have not been determined. The effects of reduced liver function on the metabolism and pharmacokinetics of tamoxifen have not been determined.

The pharmacokinetics of tamoxifen and N-desmethyl tamoxifen were characterized using a population pharmacokinetic analysis with sparse samples per patient obtained from 27 female pediatric patients aged 2 to 10 years enrolled in a study designed to evaluate the safety, efficacy, and pharmacokinetics of tamoxifen in treating McCune-Albright Syndrome. Rich data from two tamoxifen citrate pharmacokinetic trials in which 59 postmenopausal women with breast cancer completed the studies were included in the analysis to determine the structural pharmacokinetic model for tamoxifen. A one-compartment model provided the best fit to the data.

In pediatric patients, an average steady-state peak plasma concentration (C_ss, _max) and AUC were of 187 ng/mL and 4,110 ng hr/mL, respectively, and C_ss, _max occurred approximately 8 hours after dosing. Clearance (CL/F) as body weight adjusted in female pediatric patients was approximately 2.3-fold higher than in female breast cancer patients. In the youngest cohort of female pediatric patients (2 to 6 year olds), CL/F was 2.6-fold higher; in the oldest cohort (7 to 10.9 year olds) CL/F was approximately 1.9-fold higher. Exposure to N-desmethyl tamoxifen was comparable between the pediatric and adult patients. The safety and efficacy of tamoxifen for girls aged 2 to 10 years with McCune-Albright Syndrome and precocious puberty have not been studied beyond one year of treatment. The long-term effects of tamoxifen therapy in girls have not been established. In adults treated with tamoxifen an increase in incidence of uterine malignancies, stroke and pulmonary embolism has been noted (see BOXED WARNING).

Drug-Drug Interactions

In vitro studies showed that erythromycin, cyclosporin, nifedipine and diltiazem competitively inhibited formation of N-desmethyl tamoxifen with apparent K₁ of 20, 1, 45 and 30 µM, respectively. The clinical significance of these in vitro studies is unknown.

Tamoxifen reduced the plasma concentration of letrozole by 37% when these drugs were coadministered. Rifampin, a cytochrome P-450 3A4 inducer reduced tamoxifen AUC and C_max by 86% and 55%, respectively. Aminoglutethimide reduces tamoxifen and N-desmethyl tamoxifen plasma concentrations. Medroxyprogesterone reduces plasma concentrations of N-desmethyl, but not tamoxifen.

In the anastrozole adjuvant trial, coadministration of anastrozole and tamoxifen in breast cancer patients reduced anastrozole plasma concentration by 27% compared to those achieved with anastrozole alone; however, the coadministration did not affect the pharmacokinetics of tamoxifen or N-desmethyl tamoxifen (see PRECAUTIONS: Drug Interactions). Tamoxifen should not be coadministered with anastrozole.

Clinical Studies

Premenopausal Women (Tamoxifen Citrate vs. Ablation)

Three prospective, randomized studies (Ingle, Pritchard, Buchanan) compared tamoxifen to ovarian ablation (oophorectomy or ovarian irradiation) in premenopausal women with advanced breast cancer. Although the objective response rate, time to treatment failure, and survival were similar with both treatments, the limited patient accrual prevented a demonstration of equivalence. In an overview analysis of survival data from the three studies, the hazard ratio for death (tamoxifen/ovarian ablation) was 1.00 with 2-sided 95% confidence intervals of 0.73 to 1.37. Elevated serum and plasma estrogens have been observed in premenopausal women receiving tamoxifen, but the data from the randomized studies do not suggest an adverse effect of this increase. A limited number of premenopausal patients with disease progression during tamoxifen therapy responded to subsequent ovarian ablation.

Male Breast Cancer

Published results from 122 patients (119 evaluable) and case reports in 16 patients (13 evaluable) treated with tamoxifen citrate have shown that tamoxifen is effective for the palliative treatment of male breast cancer. Sixty-six of these 132 evaluable patients responded to tamoxifen which constitutes a 50% objective response rate.

Overview

The Early Breast Cancer Triauls' Collaborative Group (EBCTCG) conducted worldwide overviews of systemic adjuvant therapy for early breast cancer in 1985, 1990, and again in 1995. In 1998, 10 year outcome data were reported for 36,689 women in 55 randomized trials of adjuvant tamoxifen using doses of 20 to 40 mg/day for 1 to 5+ years. Twenty-five percent of patients received one year or less of trial treatment, 52% received 2 years, and 23% received about 5 years. Forty-eight percent of tumors were estrogen receptor (ER) positive (> 10 fmol/mg), 21% were ER poor (< 10 fmol/l), and 31% were ER unknown. Among 29,441 patients with ER positive or unknown breast cancer, 58% were entered into trials comparing tamoxifen to no adjuvant therapy and 42% were entered into trials comparing tamoxifen in combination with chemotherapy vs. the same chemotherapy alone. Among these patients, 54% had node-positive disease and 46% had node-negative disease.

Among women with ER positive or unknown breast cancer and positive nodes who received about 5 years of treatment, overall survival at 10 years was 61.4% for tamoxifen vs. 50.5% for control (logrank 2p < 0.00001). The recurrence-free rate at 10 years was 59.7% for tamoxifen vs. 44.5% for control (logrank 2p < 0.00001). Among women with ER positive or unknown breast cancer and negative nodes who received about 5 years of treatment, overall survival at 10 years was 78.9% for tamoxifen vs. 73.3% for control (logrank 2p < 0.00001). The recurrence-free rate at 10 years was 79.2% for tamoxifen vs. 64.3% for control (logrank 2p < 0.00001).

The effect of the scheduled duration of tamoxifen may be described as follows. In women with ER positive or unknown breast cancer receiving 1 year or less, 2 years or about 5 years of tamoxifen, the proportional reductions in mortality were 12%, 17% and 26%, respectively (trend significant at 2p < 0.003). The corresponding reductions in breast cancer recurrence were 21%, 29% and 47% (trend significant at 2p < 0.00001).

Benefit is less clear for women with ER poor breast cancer in whom the proportional reduction in recurrence was 10% (2p = 0.007) for all durations taken together, or 9% (2p = 0.02) if contralateral breast cancers are excluded. The corresponding reduction in mortality was 6% (NS). The effects of about 5 years of tamoxifen on recurrence and mortality were similar regardless of age and concurrent chemotherapy. There was no indication that doses greater than 20 mg per day were more effective.

Anastrozole Adjuvant ATAC Trial - Study of Anastrozole Compared to Tamoxifen for Adjuvant Treatment of Early Breast Cancer

An anastrozole adjuvant trial was conducted in 9,366 postmenopausal women with operable breast cancer who were randomized to receive adjuvant treatment with either anastrozole 1 mg daily, tamoxifen 20 mg daily, or a combination of these two treatments for 5 years or until recurrence of the disease. At a median follow-up of 33 months, the combination of anastrozole and tamoxifen did not demonstrate any efficacy benefit when compared with tamoxifen therapy alone in all patients as well as in the hormone receptor positive subpopulation. This treatment arm was discontinued from the trial. Please refer to CLINICAL PHARMACOLOGY: Special Populations: Drug-Drug Interactions, PRECAUTIONS: Laboratory Tests, PRECAUTIONS: Drug Interactions and ADVERSE REACTIONS sections for safety information from this trial. Please refer to the full prescribing information for ARIMIDEX^®† (anastrozole) 1 mg Tablets for additional information on this trial.

Patients in the two monotherapy arms of the ATAC trial were treated for a median of 60 months (5 years) and followed for a median of 68 months. Disease-free survival in the intent-to-treat population was statistically significantly improved [Hazard Ratio (HR) = 0.87, 95% CI: 0.78, 0.97, p = 0.0127] in the anastrazole arm compared to the tamoxifen arm.

Node-Positive

Node-Negative

Duration of Therapy

In the EBCTCG 1995 overview, the reduction in recurrence and mortality was greater in those studies that used tamoxifen for about 5 years than in those that used tamoxifen for a shorter period of therapy.

In the NSABP B-14 trial, in which patients were randomized to tamoxifen 20 mg/day for 5 years vs. placebo and were disease-free at the end of this 5-year period were offered rerandomization to an additional 5 years of tamoxifen or placebo. With 4 years of follow-up after this rerandomization, 92% of the women that received 5 years of tamoxifen were alive and disease-free, compared to 86% of the women scheduled to receive 10 years of tamoxifen (p = 0.003). Overall survivals were 96% and 94%, respectively (p = 0.08). Results of the B-14 study suggest that continuation of therapy beyond 5 years does not provide additional benefit.

A Scottish trial of 5 years of tamoxifen vs. indefinite treatment found a disease-free survival of 70% in the 5 year group and 61% in the indefinite group, with 6.2 years median follow-up (HR = 1.27, 95% CI 0.87 to 1.85).

In a large randomized trial conducted by the Swedish Breast Cancer Cooperative Group of adjuvant tamoxifen 40 mg/day for 2 or 5 years, overall survival at 10 years was estimated to be 80% in the patients in the 5 year tamoxifen group, compared with 74% among corresponding patients in the 2 year treatment group (p = 0.03). Disease-free survival at 10 years was 73% in the 5 year group and 67% in the 2 year group (p = 0.009). Compared with 2 years of tamoxifen treatment, 5 years of treatment resulted in a slightly greater reduction in the incidence of contralateral breast cancer at 10 years, but this difference was not statistically significant.

Contralateral Breast Cancer

The incidence of contralateral breast cancer is reduced in breast cancer patients (premenopausal and postmenopausal) receiving tamoxifen compared to placebo. Data on contralateral breast cancer are available from 32,422 out of 36,689 patients in the 1995 overview analysis of the Early Breast Cancer Triauls Collaborative Group (EBCTCG). In clinical trials with tamoxifen of 1 year or less, 2 years, and about 5 years duration, the proportional reductions in the incidence rate of contralateral breast cancer among women receiving tamoxifen were 13% (NS), 26% (2p = 0.004) and 47% (2p < 0.00001), with a significant trend favoring longer tamoxifen duration (2p = 0.008). The proportional reductions in the incidence of contralateral breast cancer were independent of age and ER status of the primary tumor. Treatment with about 5 years of tamoxifen reduced the annual incidence rate of contralateral breast cancer from 7.6 per 1,000 patients in the control group compared with 3.9 per 1,000 patients in the tamoxifen group.

In a large randomized trial in Sweden (the Stockholm Trial) of adjuvant tamoxifen 40 mg/day for 2 to 5 years, the incidence of second primary breast tumors was reduced 40% (p < 0.008) on tamoxifen compared to control. In the NSABP B-14 trial in which patients were randomized to tamoxifen 20 mg/day for 5 years vs. placebo, the incidence of second primary breast cancers was also significantly reduced (p < 0.01). In NSABP B-14, the annual rate of contralateral breast cancer was 8 per 1,000 patients in the placebo group compared with 5 per 1,000 patients in the tamoxifen group, at 10 years after first randomization.

NSABP B-24, a double-blind, randomized trial included women with ductal carcinoma in situ (DCIS). This trial compared the addition of tamoxifen or placebo to treatment with lumpectomy and radiation therapy for women with DCIS. The primary objective was to determine whether 5 years of tamoxifen therapy (20 mg/day) would reduce the incidence of invasive breast cancer in the ipsilateral (the same) or contralateral (the opposite) breast.

In this trial 1,804 women were randomized to receive either tamoxifen or placebo for 5 years: 902 women were randomized to tamoxifen 10 mg tablets twice a day and 902 women were randomized to placebo. As of December 31, 1998, follow-up data were available for 1,798 women and the median duration of follow-up was 74 months.

The tamoxifen and placebo groups were well balanced for baseline demographic and prognostic factors. Over 80% of the tumors were less than or equal to 1 cm in their maximum dimension, were not palpable, and were detected by mammography alone. Over 60% of the study population was postmenopausal. In 16% of patients, the margin of the resected specimen was reported as being positive after surgery. Approximately half of the tumors were reported to contain comedo necrosis.

For the primary endpoint, the incidence of invasive breast cancer was reduced by 43% among women assigned to tamoxifen (44 cases - tamoxifen, 74 cases - placebo; p = 0.004; relative risk (RR) = 0.57, 95% CI: 0.39 to 0.84). No data are available regarding the ER status of the invasive cancers. The stage distribution of the invasive cancers at diagnosis was similar to that reported annually in the SEER data base.

Results are shown in Table 1. For each endpoint the following results are presented: the number of events and rate per 1,000 women per year for the placebo and tamoxifen groups; and the relative risk (RR) and its associated 95% confidence interval (CI) between tamoxifen and placebo. Relative risks less than 1.0 indicate a benefit of tamoxifen therapy. The limits of the confidence intervals can be used to assess the statistical significance of the benefits of tamoxifen therapy. If the upper limit of the CI is less than 1.0, then a statistically significant benefit exists.

Table 1. Major Outcomes of the NSABP B-24 Trial

Type of Event	Lumpectomy, radiotherapy, and placebo		Lumpectomy, radiotherapy, and Tamoxifen		RR	95% CI limits
Â	No. of events	Rate per 1,000 women per year	No. of events	Rate per 1,000 women per year	Â	Â
Invasive breast cancer (Primary endpoint)	74	16.73	44	9.60	0.57	0.39 to 0.84
-Ipsilateral	47	10.61	27	5.90	0.56	0.33 to 0.91
-Contralateral	25	5.64	17	3.71	0.66	0.33 to 1.27
-Side undetermined	2	—	0	—	—
Secondary Endpoints
DCIS	56	12.66	41	8.95	0.71	0.46 to 1.08
-Ipsilateral	46	10.40	38	8.29	0.88	0.51 to 1.25
-Contralateral	10	2.26	3	0.65	0.29	0.05 to 1.13
All Breast Cancer Events	129	29.16	84	18.34	0.63	0.47 to 0.83
-All ipsilateral events	96	21.70	65	14.19	0.65	0.47 to 0.91
-All contralateral events	37	8.36	20	4.37	0.52	0.29 to 0.92
Deaths	32		28
UterineMalignanciesUpdated follow-up data (median 8.1 years)	4		9
EndometrialAdenocarcinoma	4	0.57	8	1.15
Uterine Sarcoma	0	0	1	0.14
Second primary malignancies (other than endometrial and breast)	30		29
Stroke	2		7
Thromboembolic events (DVT, PE)	5		15

Survival was similar in the placebo and tamoxifen groups. At 5 years from study entry, survival was 97% for both groups.

The Breast Cancer Prevention Trial (BCPT, NSABP P-1) was a double-blind, randomized, placebo-controlled trial with a primary objective to determine whether 5 years of tamoxifen citrate therapy (20 mg/day) would reduce the incidence of invasive breast cancer in women at high risk for the disease (see INDICATIONS AND USAGE). Secondary objectives included an evaluation of the incidence of ischemic heart disease; the effects on the incidence of bone fractures; and other events that might be associated with the use of tamoxifen, including: endometrial cancer, pulmonary embolus, deep vein thrombosis, stroke, and cataract formation and surgery (see WARNINGS).

The Gail Model was used to calculate predicted breast cancer risk for women who were less than 60 years of age and did not have lobular carcinoma in situ (LCIS). The following risk factors were used: age; number of first-degree female relatives with breast cancer; previous breast biopsies; presence or absence of atypical hyperplasia; nulliparity; age at first live birth; and age at menarche. A 5 year predicted risk of breast cancer of ≥ 1.67% was required for entry into the trial.

In this trial, 13,388 women of at least 35 years of age were randomized to receive either tamoxifen or placebo for 5 years. The median duration of treatment was 3.5 years. As of January 31, 1998, follow-up data is available for 13,114 women. Twenty-seven percent of women randomized to placebo (1,782) and 24% of women randomized to tamoxifen (1,596) completed 5 years of therapy. The demographic characteristics of women on the trial with follow-up data are shown in Table 2.

Table 2. Demographic Characteristics of Women in the NSABP P-1 Trial

Characteristic	Placebo		Tamoxifen
Â	#	%	#	%
Age (yrs.)
  35–39	184	3	158	2
  40–49	2,394	36	2,411	37
  50–59	2,011	31	2,019	31
  60–69	1,588	24	1,563	24
  ≥ 70	393	6	393	6
Age at first live birth (yrs.)
  Nulliparous	1,202	18	1,205	18
  12–19	915	14	946	15
  20–24	2,448	37	2,449	37
  25–29	1,399	21	1,367	21
  ≥ 30	606	9	577	9
Race
  White	6,333	96	6,323	96
  Black	109	2	103	2
  Other	128	2	118	2
Age at menarche
  ≥ 14	1,243	19	1,170	18
  12–13	3,610	55	3,610	55
  ≤ 11	1,717	26	1,764	27
# of first-degree relatives with breast cancer
  0	1,584	24	1,525	23
  1	3,714	57	3,744	57
  2+	1,272	19	1,275	20
Prior Hysterectomy
  No	4,173	63.5	4,018	62.4
  Yes	2,397	36.5	2,464	37.7
# of previous breast biopsies
  0	2,935	45	2,923	45
  1	1,833	28	1,850	28
  ≥ 2	1,802	27	1,771	27
History of atypical hyperplasia in the breast
  No	5,958	91	5,969	91
  Yes	612	9	575	9
History of LCIS at entry
  No	6,165	94	6,135	94
  Yes	405	6	409	6
5 year predicted breast cancer risk (%)
  ≤ 2.00	1,646	25	1,626	25
  2.01–3.00	2,028	31	2,057	31
  3.01–5.00	1,787	27	1,707	26
  ≥ 5.01	1,109	17	1,162	18
Total	6,570	100	6,544	100

Results are shown in Table 3. After a median follow-up of 4.2 years, the incidence of invasive breast cancer was reduced by 44% among women assigned to tamoxifen (86 cases-tamoxifen, 156 cases-placebo; p < 0.00001; relative risk (RR) = 0.56, 95% CI: 0.43 to 0.72). A reduction in the incidence of breast cancer was seen in each prospectively specified age group ( ≤ 49, 50 to 59, ≥ 60), in women with or without LCIS, and in each of the absolute risk levels specified in Table 3. A nonsignificant decrease in the incidence of ductal carcinoma in situ (DCIS) was seen (23-tamoxifen, 35-placebo; RR = 0.66; 95% CI: 0.39 to 1.11).

There was no statistically significant difference in the number of myocardial infarctions, severe angina, or acute ischemic cardiac events between the two groups (61-tamoxifen citrate, 59-placebo; RR = 1.04, 95% CI: 0.73 to 1.49).

No overall difference in mortality (53 deaths in tamoxifen group vs. 65 deaths in placebo group) was present. No difference in breast cancer-related mortality was observed (four deaths in tamoxifen group vs. five deaths in placebo group).

Although there was a nonsignificant reduction in the number of hip fractures (nine on tamoxifen, 20 on placebo) in the tamoxifen group, the number of wrist fractures was similar in the two treatment groups (69 on tamoxifen, 74 on placebo). A subgroup analysis of the P-1 trial, suggests a difference in effect in bone mineral density (BMD) related to menopausal status in patients receiving tamoxifen. In postmenopausal women there was no evidence of bone loss of the lumbar spine and hip. Conversely, tamoxifen was associated with significant bone loss of the lumbar spine and hip in premenopausal women.

The risks of tamoxifen therapy include endometrial cancer, DVT, PE, stroke, cataract formation, and cataract surgery (see Table 3). In the NSABP P-1 trial, 33 cases of endometrial cancer were observed in the tamoxifen group vs. 14 in the placebo group (RR = 2.48, 95% CI: 1.27 to 4.92). Deep vein thrombosis was observed in 30 women receiving tamoxifen vs. 19 in women receiving placebo (RR = 1.59, 95% CI: 0.86 to 2.98). Eighteen cases of pulmonary embolism were observed in the tamoxifen group vs. six in the placebo group (RR = 3.01, 95% CI: 1.15 to 9.27). There were 34 strokes on the tamoxifen arm and 24 on the placebo arm (RR = 1.42, 95% CI: 0.82 to 2.51). Cataract formation in women without cataracts at baseline was observed in 540 women taking tamoxifen vs. 483 women receiving placebo (RR = 1.13, 95% CI: 1.00 to 1.28). Cataract surgery (with or without cataracts at baseline) was performed in 201 women taking tamoxifen vs. 129 women receiving placebo (RR = 1.51, 95% CI: 1.21 to 1.89) (see WARNINGS).

Table 3 summarizes the major outcomes of the NSABP P-1 trial. For each endpoint, the following results are presented: the number of events and rate per 1,000 women per year for the placebo and tamoxifen groups; and the relative risk (RR) and its associated 95% confidence interval (CI) between tamoxifen and placebo. Relative risks less than 1.0 indicate a benefit of tamoxifen therapy. The limits of the confidence intervals can be used to assess the statistical significance of the benefits or risks of tamoxifen therapy. If the upper limit of the CI is less than 1.0, then a statistically significant benefit exists.

For most participants, multiple risk factors would have been required for eligibility. This table considers risk factors individually, regardless of other coexisting risk factors, for women who developed breast cancer. The 5 year predicted absolute breast cancer risk accounts for multiple risk factors in an individual and should provide the best estimate of individual benefit (see INDICATIONS AND USAGE).

Table 3. Major Outcomes of the NSABP P-1 Trial

Â	# Of Events		Rate/1,000 Women/Year			95% CI
TYPE OF EVENT	PLACEBO	TAMOXIFEN	PLACEBO	TAMOXIFEN	RR	LIMITS
Invasive Breast Cancer	156	86	6.49	3.58	0.56	0.43–0.72
  Age ≤ 49	59	38	6.34	4.11	0.65	0.43–0.98
  Age 50–59	46	25	6.31	3.53	0.56	0.35–0.91
  Age ≥ 60	51	23	7.17	3.22	0.45	0.27–0.74
Risk Factors for Breast Cancer History, LCIS
  No	140	78	6.23	3.51	0.56	0.43–0.74
  Yes	16	8	12.73	6.33	0.50	0.21–1.17
History, Atypical Hyperplasia
  No	138	84	6.37	3.89	0.61	0.47–0.80
  Yes	18	2	8.69	1.05	0.12	0.03–0.52
No. First-Degree Relatives
  0	32	17	5.97	3.26	0.55	0.30–0.98
  1	80	45	5.81	3.31	0.57	0.40–0.82
  2	35	18	8.92	4.67	0.52	0.30–0.92
  ≥ 3	9	6	13.33	7.58	0.57	0.20–1.59
5 Year Predicted Breast Cancer Risk (as calculated by the Gail Model)
  ≤ 2.00%	31	13	5.36	2.26	0.42	0.22–0.81
  2.01–3.00%	39	28	5.25	3.83	0.73	0.45–1.18
  3.01–5.00%	36	26	5.37	4.06	0.76	0.46–1.26
  ≥ 5.00%	50	19	13.15	4.71	0.36	0.21–0.61
DCIS	35	23	1.47	0.97	0.66	0.39–1.11
Fractures (protocol-specified sites)	92Two women had hip and wrist fractures	76	3.87	3.20	0.61	0.83–1.12
  Hip	20	9	0.84	0.38	0.45	0.18–1.04
  WristIncludes Colles' and other lower radius fractures	74	69	3.11	2.91	0.93	0.67–1.29
Total Ischemic Events	59	61	2.47	2.57	1.04	0.71–1.51
  Myocardial Infarction	27	27	1.13	1.13	1.00	0.57–1.78
    Fatal	8	7	0.33	0.29	0.88	0.27–2.77
    Nonfatal	19	20	0.79	0.84	1.06	0.54–2.09
  AnginaRequiring angioplasty or CABG	12	12	0.50	0.50	1.00	0.41–2.44
  Acute Ischemic SyndromeNew Q-wave on ECG; no angina or elevation of serum enzymes; or angina requiring hospitalization without surgery	20	22	0.84	0.92	1.11	0.58–2.13
Uterine
  Malignancies (among    women with an    intact uterus)Updated long-term follow-up data (median 6.9 years) from NSABP P-1 study added after cut-off for the other information in this table.	17	57
  Endometrial    Adenocarcinoma	17	53	0.71	2.20
  Uterine Sarcoma	0	4	0.0	0.17
Stroke Seven cases were fatal; three in the placebo group and four in the tamoxifen group	24	34	1.00	1.43	1.42	0.82–2.51
Transient Ischemic Attack	21	18	0.88	0.75	0.86	0.43–1.70
Pulmonary Emboli Three cases in the tamoxifen group were fatal	6	18	0.25	0.75	3.01	1.15–9.27
Deep Vein Thrombosis All but three cases in each group required hospitalization	19	30	0.79	1.26	1.59	0.86–2.98
Cataracts Developing on Study Based on women without cataracts at baseline (6,230-Placebo, 6,199-tamoxifen)	483	540	22.51	25.41	1.13	1.00–1.28
Underwent Cataract Surgery	63	101	2.83	4.57	1.62	1.18–2.22
Underwent Cataract Surgery All women (6,707-Placebo, 6,681-tamoxifen)	129	201	5.44	8.56	1.58	1.26–1.97

Table 4 describes the characteristics of the breast cancers in the NSABP P-1 trial and includes tumor size, nodal status, ER status. Tamoxifen decreased the incidence of small estrogen receptor positive tumors, but did not alter the incidence of estrogen receptor negative tumors or larger tumors.

Table 4. Characteristics of Breast Cancer in NSABP P-1 Trial

Staging Parameter	Placebo N = 156	Tamoxifen N = 86	Total N = 242
Tumor size:
T1	117	60	177
T2	28	20	48
T3	7	3	10
T4	1	2	3
Unknown	3	1	4
Nodal status:
Negative	103	56	159
1–3 positive nodes	29	14	43
≥ 4 positive nodes	10	12	22
Unknown	14	4	18
Stage:
I	88	47	135
II: node-negative	15	9	24
II: node-positive	33	22	55
III	6	4	10
IV	2One participant presented with a suspicious bone scan but did not have documented metastases. She subsequently died of metastatic breast cancer.	1	3
Unknown	12	3	15
Estrogen receptor:
Positive	115	38	153
Negative	27	36	63
Unknown	14	12	26

Interim results from two trials in addition to the NSABP P-1 trial examining the effects of tamoxifen in reducing breast cancer incidence have been reported.

The first was the Italian Tamoxifen Prevention trial. In this trial women between the ages of 35 and 70, who had had a total hysterectomy, were randomized to receive 20 mg tamoxifen or matching placebo for 5 years. The primary endpoints were occurrence of, and death from, invasive breast cancer. Women without any specific risk factors for breast cancer were to be entered. Between 1992 and 1997, 5408 women were randomized. Hormone Replacement Therapy (HRT) was used in 14% of participants. The trial closed in 1997 due to the large number of dropouts during the first year of treatment (26%). After 46 months of follow-up there were 22 breast cancers in women on placebo and 19 in women on tamoxifen. Although no decrease in breast cancer incidence was observed, there was a trend for a reduction in breast cancer among women receiving protocol therapy for at least one year (19-placebo, 11-tamoxifen). The small numbers of participants along with the low level of risk in this otherwise healthy group precluded an adequate assessment of the effect of tamoxifen in reducing the incidence of breast cancer.

The second trial, the Royal Marsden Trial (RMT) was reported as an interim analysis. The RMT was begun in 1986 as a feasibility study of whether larger scale trials could be mounted. The trial was subsequently extended to a pilot trial to accrue additional participants to further assess the safety of tamoxifen. Twenty-four hundred and seventy-one women were entered between 1986 and 1996; they were selected on the basis of a family history of breast cancer. HRT was used in 40% of participants. In this trial, with a 70 month median follow-up, 34 and 36 breast cancers (eight noninvasive, four on each arm) were observed among women on tamoxifen and placebo, respectively. Patients in this trial were younger than those in the NSABP P-1 trial and may have been more likely to develop ER (-) tumors, which are unlikely to be reduced in number by tamoxifen therapy. Although women were selected on the basis of family history and were thought to have a high risk of breast cancer, few events occurred, reducing the statistical power of the study. These factors are potential reasons why the RMT may not have provided an adequate assessment of the effectiveness of tamoxifen in reducing the incidence of breast cancer.

In these trials, an increased number of cases of deep vein thrombosis, pulmonary embolus, stroke, and endometrial cancer were observed on the tamoxifen arm compared to the placebo arm. The frequency of events was consistent with the safety data observed in the NSABP P-1 trial.

A single, uncontrolled multicenter trial of tamoxifen 20 mg once a day was conducted in a heterogenous group of girls with McCune-Albright Syndrome and precocious puberty manifested by physical signs of pubertal development, episodes of vaginal bleeding and/or advanced bone age (bone age of at least 12 months beyond chronological age). Twenty-eight female pediatric patients, aged 2 to 10 years, were treated for up to 12 months. Effect of treatment on frequency of vaginal bleeding, bone age advancement, and linear growth rate was assessed relative to prestudy baseline. Tamoxifen treatment was associated with a 50% reduction in frequency of vaginal bleeding episodes by patient or family report (mean annualized frequency of 3.56 episodes at baseline and 1.73 episodes on-treatment). Among the patients who reported vaginal bleeding during the prestudy period, 62% (13 out of 21 patients) reported no bleeding for a 6-month period and 33% (7 out of 21 patients) reported no vaginal bleeding for the duration of the trial. Not all patients improved on treatment and a few patients not reporting vaginal bleeding in the 6 months prior to enrollment reported menses on treatment. Tamoxifen therapy was associated with a reduction in mean rate of increase of bone age. Individual responses with regard to bone age advancement were highly heterogeneous. Linear growth rate was reduced during the course of tamoxifen treatment in a majority of patients (mean change of 1.68 cm/year relative to baseline; change from 7.47 cm/year at baseline to 5.79 cm/year on study). This change was not uniformly seen across all stages of bone maturity; all recorded response failures occurred in patients with bone ages less than 7 years at screening.

Mean uterine volume increased after 6 months of treatment and doubled at the end of the one-year study. A causal relationship has not been established; however, as an increase in the incidence of endometrial adenocarcinoma and uterine sarcoma has been noted in adults treated with tamoxifen (see BOXED WARNING), continued monitoring of McCune-Albright patients treated with tamoxifen for long-term uterine effects is recommended. The safety and efficacy of tamoxifen for girls aged 2 to 10 years with McCune-Albright Syndrome and precocious puberty have not been studied beyond one year of treatment. The long-term effects of tamoxifen therapy in girls have not been established.

Indications And Usage

Metastatic Breast Cancer

Tamoxifen citrate tablets are effective in the treatment of metastatic breast cancer in women and men. In premenopausal women with metastatic breast cancer, tamoxifen citrate tablets are an alternative to oophorectomy or ovarian irradiation. Available evidence indicates that patients whose tumors are estrogen receptor positive are more likely to benefit from tamoxifen citrate tablet therapy.

Adjuvant Treatment of Breast Cancer

Tamoxifen citrate tablets are indicated for the treatment of node-positive breast cancer in postmenopausal women following total mastectomy or segmental mastectomy, axillary dissection, and breast irradiation. In some tamoxifen adjuvant studies, most of the benefit to date has been in the subgroup with four or more positive axillary nodes.

Tamoxifen citrate tablets are indicated for the treatment of axillary node-negative breast cancer in women following total mastectomy or segmental mastectomy, axillary dissection, and breast irradiation.

The estrogen- and progesterone-receptor values may help to predict whether adjuvant tamoxifen citrate tablet therapy is likely to be beneficial.

Tamoxifen citrate tablets reduce the occurrence of contralateral breast cancer in patients receiving adjuvant tamoxifen citrate tablet therapy for breast cancer.

Ductal Carcinoma in Situ (DCIS)

In women with DCIS, following breast surgery and radiation, tamoxifen citrate tablets are indicated to reduce the risk of invasive breast cancer (see BOXED WARNING). The decision regarding therapy with tamoxifen citrate tablets for the reduction in breast cancer incidence should be based upon an individual assessment of the benefits and risks of tamoxifen citrate tablet therapy.

Current data from clinical trials support 5 years of adjuvant tamoxifen citrate tablet therapy for patients with breast cancer.

Reduction in Breast Cancer Incidence in High Risk Women

Tamoxifen citrate tablets are indicated to reduce the incidence of breast cancer in women at high risk for breast cancer. This effect was shown in a study of 5 years planned duration with a median follow-up of 4.2 years. Twenty-five percent of the participants received drug for 5 years. The longer-term effects are not known. In this study, there was no impact of tamoxifen citrate tablets on overall or breast cancer-related mortality (see BOXED WARNING).

Tamoxifen citrate tablets are indicated only for high risk women. "High risk" is defined as women at least 35 years of age with a 5 year predicted risk of breast cancer ≥ 1.67%, as calculated by the Gail Model.

Examples of combinations of factors predicting a 5 year risk ≥ 1.67% are:

Age 35 or older and any of the following combination of factors:

• •One first-degree relative with a history of breast cancer, two or more benign biopsies, and a history of a breast biopsy showing atypical hyperplasia; or
• •At least two first-degree relatives with a history of breast cancer, and a personal history of at least one breast biopsy; or
• •LCIS

Age 40 or older and any of the following combination of factors:

• •One first-degree relative with a history of breast cancer, two or more benign biopsies, age at first live birth 25 or older, and age at menarche 11 or younger; or
• •At least two first-degree relatives with a history of breast cancer, and age at first live birth 19 or younger; or
• •One first-degree relative with a history of breast cancer, and a personal history of a breast biopsy showing atypical hyperplasia.

Age 45 or older and any of the following combination of factors:

• •At least two first-degree relatives with a history of breast cancer and age at first live birth 24 or younger; or
• •One first-degree relative with a history of breast cancer with a personal history of a benign breast biopsy, age at menarche 11 or less and age at first live birth 20 or more.

Age 50 or older and any of the following combination of factors:

• •At least two first-degree relatives with a history of breast cancer; or
• •History of one breast biopsy showing atypical hyperplasia, and age at first live birth 30 or older and age at menarche 11 or less; or
• •History of at least two breast biopsies with a history of atypical hyperplasia, and age at first live birth 30 or more.

Age 55 or older and any of the following combination of factors:

• •One first-degree relative with a history of breast cancer with a personal history of a benign breast biopsy, and age at menarche 11 or less; or
• •History of at least two breast biopsies with a history of atypical hyperplasia, and age at first live birth 20 or older.

Age 60 or older and:

• •5 year predicted risk of breast cancer ≥ 1.67%, as calculated by the Gail Model.

For women whose risk factors are not described in the above examples, the Gail Model is necessary to estimate absolute breast cancer risk. Healthcare Professionals can obtain a Gail Model Risk Assessment Tool by dialing Mylan Pharmaceuticals Inc. at 1-877-446-3679 (1-877-4-INFO-RX).

There are insufficient data available regarding the effect of tamoxifen citrate tablets on breast cancer incidence in women with inherited mutations (BRCA1, BRCA2) to be able to make specific recommendations on the effectiveness of tamoxifen in these patients.

After an assessment of the risk of developing breast cancer, the decision regarding therapy with tamoxifen citrate tablets for the reduction in breast cancer incidence should be based upon an individual assessment of the benefits and risks of tamoxifen citrate tablet therapy. In the NSABP P-1 trial, tamoxifen citrate tablet treatment lowered the risk of developing breast cancer during the follow-up period of the trial, but did not eliminate breast cancer risk (see CLINICAL PHARMACOLOGY: Table 3).

Contraindications

Tamoxifen citrate tablets are contraindicated in patients with known hypersensitivity to the drug or any of its ingredients.

Reduction in Breast Cancer Incidence in High Risk Women and Women with DCIS

Tamoxifen citrate tablets are contraindicated in women who require concomitant coumarin-type anticoagulant therapy or in women with a history of deep vein thrombosis or pulmonary embolus.

Warnings

Effects in Metastatic Breast Cancer Patients

As with other additive hormonal therapy (estrogens and androgens), hypercalcemia has been reported in some breast cancer patients with bone metastases within a few weeks of starting treatment with tamoxifen. If hypercalcemia does occur, appropriate measures should be taken and, if severe, tamoxifen should be discontinued.

Effects on the Uterus

An increased incidence of uterine malignancies has been reported in association with tamoxifen treatment. The underlying mechanism is unknown, but may be related to the estrogen-like effect of tamoxifen. Most uterine malignancies seen in association with tamoxifen are classified as adenocarcinoma of the endometrium. However, rare uterine sarcomas, including malignant mixed mullerian tumors (MMMT), have also been reported. Uterine sarcoma is generally associated with a higher FIGO stage (III/IV) at diagnosis, poorer prognosis, and shorter survival. Uterine sarcoma has been reported to occur more frequently among long-term users ( ≥ 2 years) of tamoxifen than non-users. Some of the uterine malignancies (endometrial carcinoma or uterine sarcoma) have been fatal.

In the NSABP P-1 trial, among participants randomized to tamoxifen there was a statistically significant increase in the incidence of endometrial cancer (33 cases of invasive endometrial cancer, compared to 14 cases among participants randomized to placebo (RR = 2.48, 95% CI: 1.27 to 4.92). The 33 cases in participants receiving tamoxifen were FIGO Stage I, including 20 IA, 12 IB, and 1 IC endometrial adenocarcinomas. In participants randomized to placebo, 13 were FIGO Stage I (8 IA and 5 IB) and 1 was FIGO Stage IV. Five women on tamoxifen and one on placebo received postoperative radiation therapy in addition to surgery. This increase was primarily observed among women at least 50 years of age at the time of randomization (26 cases of invasive endometrial cancer, compared to six cases among participants randomized to placebo (RR = 4.50, 95% CI: 1.78 to 13.16). Among women ≤ 49 years of age at the time of randomization there were seven cases of invasive endometrial cancer, compared to eight cases among participants randomized to placebo (RR = 0.94, 95% CI: 0.28 to 2.89). If age at the time of diagnosis is considered, there were four cases of endometrial cancer among participants ≤ 49 randomized to tamoxifen compared to two among participants randomized to placebo (RR = 2.21, 95% CI: 0.4 to 12.0). For women ≥ 50 at the time of diagnosis, there were 29 cases among participants randomized to tamoxifen compared to 12 among women on placebo (RR = 2.5, 95% CI: 1.3 to 4.9). The risk ratios were similar in the two groups, although fewer events occurred in younger women. Most (29 of 33 cases in the tamoxifen group) endometrial cancers were diagnosed in symptomatic women, although 5 of 33 cases in the tamoxifen group occurred in asymptomatic women. Among women receiving tamoxifen the events appeared between 1 and 61 months (average = 32 months) from the start of treatment.

In an updated review of long-term data (median length of total follow-up is 6.9 years, including blinded follow-up) on 8,306 women with an intact uterus at randomization in the NSABP P-1 risk reduction trial, the incidence of both adenocarcinomas and rare uterine sarcomas was increased in women taking tamoxifen. During blinded follow-up, there were 36 cases of FIGO Stage I endometrial adenocarcinoma (22 were FIGO Stage IA, 13 IB, and 1 IC) in women receiving tamoxifen and 15 cases in women receiving placebo [14 were FIGO Stage I (9 IA and 5 IB), and one case was FIGO Stage IV]. Of the patients receiving tamoxifen who developed endometrial cancer, one with Stage IA and 4 with Stage IB cancers received radiation therapy. In the placebo group, one patient with FIGO Stage IB cancer received radiation therapy and the patient with FIGO Stage IVB cancer received chemotherapy and hormonal therapy. During total follow-up, endometrial adenocarcinoma was reported in 53 women randomized to tamoxifen (30 cases of FIGO Stage IA, 20 were Stage IB, 1 was Stage IC, and two were Stage IIIC) and 17 women randomized to placebo (nine cases were FIGO Stage IA, six were Stage IB, one was Stage IIIC, and one was Stage IVB (incidence per 1,000 women-years of 2.20 and 0.71, respectively). Some patients received postoperative radiation therapy in addition to surgery. Uterine sarcomas were reported in four women randomized to tamoxifen (one was FIGO IA, one was FIGO IB, one was FIGO IIA, and one was FIGO IIIC) and one patient randomized to placebo (FIGO IA); incidence per 1,000 women-years of 0.17 and 0.04, respectively. Of the patients randomized to tamoxifen, the FIGO IA and IB cases were a MMMT and sarcoma, respectively; the FIGO II was a MMMT; and the FIGO III was a sarcoma; and the one patient randomized to placebo had a MMMT. A similar increased incidence in endometrial adenocarcinoma and uterine sarcoma was observed among women receiving tamoxifen in five other NSABP clinical trials.

Any patient receiving or who has previously received tamoxifen who reports abnormal vaginal bleeding should be promptly evaluated. Patients receiving or who have previously received tamoxifen should have annual gynecological examinations and they should promptly inform their physicians if they experience any abnormal gynecological symptoms, e.g., menstrual irregularities, abnormal vaginal bleeding, changes in vaginal discharge, or pelvic pain or pressure.

In the P-1 trial, endometrial sampling did not alter the endometrial cancer detection rate compared to women who did not undergo endometrial sampling (0.6% with sampling, 0.5% without sampling) for women with an intact uterus. There are no data to suggest that routine endometrial sampling in asymptomatic women taking tamoxifen to reduce the incidence of breast cancer would be beneficial.

Non-Malignant Effects on the Uterus

An increased incidence of endometrial changes including hyperplasia and polyps have been reported in association with tamoxifen treatment. The incidence and pattern of this increase suggest that the underlying mechanism is related to the estrogenic properties of tamoxifen.

There have been a few reports of endometriosis and uterine fibroids in women receiving tamoxifen. The underlying mechanism may be due to the partial estrogenic effect of tamoxifen. Ovarian cysts have also been observed in a small number of premenopausal patients with advanced breast cancer who have been treated with tamoxifen.

Tamoxifen has been reported to cause menstrual irregularity or amenorrhea.

Thromboembolic Effects of Tamoxifen

There is evidence of an increased incidence of thromboembolic events, including deep vein thrombosis and pulmonary embolism, during tamoxifen therapy. When tamoxifen is coadministered with chemotherapy, there may be a further increase in the incidence of thromboembolic effects. For treatment of breast cancer, the risks and benefits of tamoxifen should be carefully considered in women with a history of thromboembolic events. In a small substudy (N = 81) of the NSABP P-1 trial, there appeared to be no benefit to screening women for Factor V Leiden and Prothrombin mutations G20210A as a means to identify those who may not be appropriate candidates for tamoxifen therapy.

Data from the NSABP P-1 trial show that participants receiving tamoxifen without a history of pulmonary emboli (PE) had a statistically significant increase in pulmonary emboli (18-tamoxifen, 6-placebo, RR = 3.01, 95% CI: 1.15 to 9.27). Three of the pulmonary emboli, all in the tamoxifen arm, were fatal. Eighty-seven percent of the cases of pulmonary embolism occurred in women at least 50 years of age at randomization. Among women receiving tamoxifen, the events appeared between 2 and 60 months (average = 27 months) from the start of treatment.

In this same population, a non-statistically significant increase in deep vein thrombosis (DVT) was seen in the tamoxifen group (30-tamoxifen, 19-placebo; RR = 1.59, 95% CI: 0.86 to 2.98). The same increase in relative risk was seen in women ≤ 49 and in women ≥ 50, although fewer events occurred in younger women. Women with thromboembolic events were at risk for a second related event (seven out of 25 women on placebo, five out of 48 women on tamoxifen) and were at risk for complications of the event and its treatment (0/25 on placebo, 4/48 on tamoxifen). Among women receiving tamoxifen, deep vein thrombosis events occurred between 2 and 57 months (average = 19 months) from the start of treatment.

There was a non-statistically significant increase in stroke among patients randomized to tamoxifen (24-placebo; 34-tamoxifen; RR = 1.42; 95% CI: 0.82 to 2.51). Six of the 24 strokes in the placebo group were considered hemorrhagic in origin and 10 of the 34 strokes in the tamoxifen group were categorized as hemorrhagic. Seventeen of the 34 strokes in the tamoxifen group were considered occlusive and seven were considered to be of unknown etiology. Fourteen of the 24 strokes on the placebo arm were reported to be occlusive and four of unknown etiology. Among these strokes three strokes in the placebo group and four strokes in the tamoxifen group were fatal. Eighty-eight percent of the strokes occurred in women at least 50 years of age at the time of randomization. Among women receiving tamoxifen, the events occurred between 1 and 63 months (average = 30 months) from the start of treatment.

Effects on the Liver: Liver Cancer

In the Swedish trial using adjuvant tamoxifen 40 mg/day for 2 to 5 years, three cases of liver cancer have been reported in the tamoxifen-treated group vs. one case in the observation group (see PRECAUTIONS: Carcinogenesis). In other clinical trials evaluating tamoxifen, no cases of liver cancer have been reported to date.

One case of liver cancer was reported in NSABP P-1 in a participant randomized to tamoxifen.

Effects on the Liver: Non-Malignant Effects

Tamoxifen has been associated with changes in liver enzyme levels, and on rare occasions, a spectrum of more severe liver abnormalities including fatty liver, cholestasis, hepatitis and hepatic necrosis. A few of these serious cases included fatalities. In most reported cases the relationship to tamoxifen is uncertain. However, some positive rechallenges and dechallenges have been reported.

In the NSABP P-1 trial, few grade 3 to 4 changes in liver function (SGOT, SGPT, bilirubin, alkaline phosphatase) were observed (10 on placebo and six on tamoxifen). Serum lipids were not systematically collected.

Other Cancers

A number of second primary tumors, occurring at sites other than the endometrium, have been reported following the treatment of breast cancer with tamoxifen in clinical trials. Data from the NSABP B-14 and P-1 studies show no increase in other (non-uterine) cancers among patients receiving tamoxifen. Whether an increased risk for other (non-uterine) cancers is associated with tamoxifen is still uncertain and continues to be evaluated.

Effects on the Eye

Ocular disturbances, including corneal changes, decrement in color vision perception, retinal vein thrombosis, and retinopathy have been reported in patients receiving tamoxifen. An increased incidence of cataracts and the need for cataract surgery have been reported in patients receiving tamoxifen.

In the NSABP P-1 trial, an increased risk of borderline significance of developing cataracts among those women without cataracts at baseline (540-tamoxifen; 483-placebo; RR = 1.13, 95% CI: 1.00 to 1.28) was observed. Among these same women, tamoxifen was associated with an increased risk of having cataract surgery (101-tamoxifen; 63-placebo; RR = 1.62, 95% CI 1.18 to 2.22) (see CLINICAL PHARMACOLOGY: Table 3). Among all women on the trial (with or without cataracts at baseline), tamoxifen was associated with an increased risk of having cataract surgery (201-tamoxifen; 129-placebo; RR = 1.58, 95% CI 1.26 to 1.97). Eye examinations were not required during the study. No other conclusions regarding non-cataract ophthalmic events can be made.

Pregnancy

Tamoxifen may cause fetal harm when administered to a pregnant woman. Women should be advised not to become pregnant while taking tamoxifen or within 2 months of discontinuing tamoxifen and should use barrier or nonhormonal contraceptive measures if sexually active. Tamoxifen does not cause infertility, even in the presence of menstrual irregularity. Effects on reproductive functions are expected from the antiestrogenic properties of the drug. In reproductive studies in rats at dose levels equal to or below the human dose, nonteratogenic developmental skeletal changes were seen and were found reversible. In addition, in fertility studies in rats and in teratology studies in rabbits using doses at or below those used in humans, a lower incidence of embryo implantation and a higher incidence of fetal death or retarded in utero growth were observed, with slower learning behavior in some rat pups when compared to historical controls. Several pregnant marmosets were dosed with 10 mg/kg/day (about 2-fold the daily maximum recommended human dose on a mg/m² basis) during organogenesis or in the last half of pregnancy. No deformations were seen and, although the dose was high enough to terminate pregnancy in some animals, those that did maintain pregnancy showed no evidence of teratogenic malformations.

In rodent models of fetal reproductive tract development, tamoxifen (at doses 0.002-fold to 2.4-fold the daily maximum recommended human dose on a mg/m² basis) caused changes in both sexes that are similar to those caused by estradiol, ethynylestradiol and diethylstilbestrol. Although the clinical relevance of these changes is unknown, some of these changes, especially vaginal adenosis, are similar to those seen in young women who were exposed to diethylstilbestrol in utero and who have a 1 in 1,000 risk of developing clear-cell adenocarcinoma of the vagina or cervix. To date, in utero exposure to tamoxifen has not been shown to cause vaginal adenosis, or clear-cell adenocarcinoma of the vagina or cervix, in young women. However, only a small number of young women have been exposed to tamoxifen in utero, and a smaller number have been followed long enough (to age 15 to 20) to determine whether vaginal or cervical neoplasia could occur as a result of this exposure.

There are no adequate and well controlled trials of tamoxifen in pregnant women. There have been a small number of reports of vaginal bleeding, spontaneous abortions, birth defects, and fetal deaths in pregnant women. If this drug is used during pregnancy, or the patient becomes pregnant while taking this drug, or within approximately 2 months after discontinuing therapy, the patient should be apprised of the potential risks to the fetus including the potential long-term risk of a DES-like syndrome.

Reduction in Breast Cancer Incidence in High Risk Women

For sexually active women of childbearing potential, tamoxifen therapy should be initiated during menstruation. In women with menstrual irregularity, a negative B-HCG immediately prior to the initiation of therapy is sufficient (see PRECAUTIONS: Information for Patients: Reduction in Breast Cancer Incidence in High Risk Women).