(Refer to the Letrozole section in the Aromatase inhibitors section of this summary for more information.)
Tamoxifen and chemotherapy
That chemotherapy should add to the effect of tamoxifen in postmenopausal women has been postulated.[91,92] In a trial (NSABP-B-16) of node-positive women older than 50 years with hormone receptor–positive tumors, 3-year DFS and OS rates were better in those who received doxorubicin, cyclophosphamide, and tamoxifen versus tamoxifen alone (DFS was 84% vs. 67%; P = .004; OS was 93% vs. 85%; P = .04).[Level of evidence: 1iiA] The NSABP-B-20 study compared tamoxifen alone with tamoxifen plus chemotherapy (cyclophosphamide, methotrexate, and fluorouracil [5-FU] [CMF] or sequential methotrexate and 5-FU) in women with node-negative, ER-positive breast cancer. After 12 years of follow-up, the chemotherapy plus tamoxifen regimen resulted in 89% DFS and 87% OS compared with a 79% DFS and 83% OS with tamoxifen alone.[Level of evidence: 1iiA]
In another study of postmenopausal women with node-positive disease, tamoxifen alone was compared with tamoxifen plus three different schedules of CMF. A small, DFS advantage was conferred by the addition of early CMF to tamoxifen in women with ER-positive disease.[Level of evidence: 1iiDii] However, another study in a similar patient population, in which women were randomly assigned to receive adjuvant tamoxifen with or without CMF, showed no benefit in the chemotherapy arm; in this study, intravenous (day 1 every 3 weeks) rather than oral cyclophosphamide was used.[Level of evidence: 1iiA] The overall results of the available evidence suggest that the addition of chemotherapy to tamoxifen in postmenopausal women with ER-positive disease results in a significant, but small, survival advantage.
Tamoxifen toxic effects
The use of adjuvant tamoxifen has been associated with certain toxic effects. The most important effect is the development of endometrial cancer which, in large clinical trials, has been reported to occur at a rate that is two times to seven times greater than that observed in untreated women.[97,98,99,100] Women taking tamoxifen should be evaluated by a gynecologist if they experience any abnormal uterine bleeding. Although one retrospective study raised concern that endometrial cancers in women taking tamoxifen (40 mg/day) had a worse outcome and were characterized by higher-grade lesions and a more advanced stage than endometrial cancers in women not treated with tamoxifen, other larger studies using standard tamoxifen doses (20 mg/day) have not supported this finding.[97,101,102] Similar to estrogen, tamoxifen produces endometrial hyperplasia, which can be a premalignant change. In a cohort of women without a history of breast cancer who were randomly assigned to receive tamoxifen or placebo on the British Pilot Breast Cancer Prevention Trial, 16% of those on tamoxifen developed atypical hyperplasia at varying times from the start of treatment (range, 3 months–75 months; median, 24 months), while no cases occurred on the control arm. The value of endometrial biopsy, hysteroscopy, and transvaginal ultrasound as screening tools is unclear.[104,105] Of concern is an increased risk of gastrointestinal malignancy after tamoxifen therapy, but these findings are tentative, and further study is needed.