Results and implications of the Royal Marsden and other tamoxifen chemoprevention trials: an alternative view

Incidence of invasive breast cancer in postmenopausal women after discontinuation of long-term raloxifene administration

BACKGROUND

Postmenopausal women with osteoporosis had a 66% relative risk reduction for invasive breast cancer over 8 years of raloxifene therapy in the randomized, placebo-controlled 4-year MORE (Multiple Outcomes of Raloxifene Evaluation) trial and the CORE (Continuing Outcomes Relevant to Evista) trial, a 4-year follow-up to MORE.

PATIENTS AND METHODS

The first post hoc analysis examined the effects of raloxifene on the cumulative incidence of invasive breast cancer on a yearly basis. Another analysis compared the incidence of invasive breast cancer in 3967 patients who continued raloxifene for 8 years (RLX-C, n = 2280), discontinued raloxifene after 4 years in MORE (RLX-D, n = 401), or took placebo (n = 1286) for a mean 2.9 years' treatment duration (57,338 patient-years).

RESULTS

The unadjusted breast cancer incidence rate was 5.39 per 1000 patient-years in the placebo group compared with 2.26 in the RLX-C group (hazard ratio [HR], 0.41 [95% CI 0.21-0.81]) and 3.59 in the RLX-D group (HR, 0.69 [95% CI 0.23-2.01]). Because the choice of taking the study drug was not randomized in CORE, propensity scores were used to adjust for potential imbalances in baseline characteristics before CORE. Results after adjustment by the propensity score method were similar to the unadjusted results.

CONCLUSION

This analysis suggests a persistent effect for breast cancer risk reduction in patients who discontinued raloxifene, although this conclusion is limited by the small sample size.

Prevention of Hormone-Related Cancers: Breast Cancer

Carcinogenesis in the breast is a hormonally dependent process. Evidence implicating estrogen as a key breast carcinogen comes from various lines of investigation. Traditional epidemiologic studies demonstrate associations between estrogen exposure, both exogenous and endogenous, and increased breast cancer risk. Ongoing genetic epidemiologic studies also show associations between specific polymorphisms in estrogen-metabolizing genes and risk, albeit inconsistently. The application of these findings to the treatment and, more recently, the prevention of breast cancer has led to the development of agents that either (1) inhibit estrogen action at the estrogen receptor (selective estrogen receptor modulators (SERMs]); or (2) inhibit estrogen-synthesizing enzymes, thereby abrogating synthesis of this hormone (aromatase inhibitors). Large phase III trials have evaluated the ability of such agents to reduce the incidence of breast cancer in women at increased risk of the disease. The National Surgical Adjuvant Breast and Bowel Project (NSABP) P-1: Breast Cancer Prevention Trial (BCPT) demonstrated the superiority of the SERM tamoxifen to placebo in reducing breast cancer risk, leading to the Food and Drug Administration approval of tamoxifen for risk reduction. The implementation of tamoxifen for this indication has not become widespread in clinical practice, however, for a variety of reasons that we discuss. Results from the NSABP Study of Tamoxifen and Raloxifene, which compares the risk-reducing efficacy as well as toxicity of these two SERMs in a similar high-risk population, will be available in the near future. Based on promising data involving reduction of contralateral breast cancer risk in adjuvant studies, several aromatase inhibitors, including letrozole, anastrozole, and exemestane, are being incorporated into trials evaluating their efficacy as preventive agents in women at increased risk.

Tamoxifen for prevention of breast cancer

OBJECTIVE

To review data on the use of tamoxifen for primary prevention of breast cancer.

DATA SOURCES

A literature search was performed through MEDLINE (1992-May 2002) using the key words tamoxifen, breast cancer, and prevention.

DATA SYNTHESIS

Breast cancer is the most common malignancy detected in American women. Attempts to reduce morbidity and mortality include early detection programs and chemoprevention. Clinical trials of tamoxifen for reduction of breast cancer risk are reviewed.

CONCLUSIONS

Tamoxifen may reduce the risk of primary breast cancer in women at increased risk. The benefit of tamoxifen in women who are not at risk is uncertain. The risks of developing thromboembolic disorders or endometrial cancer must be considered before tamoxifen is prescribed. Women should be given all of the information about the benefits and risks of tamoxifen use so that they can make an informed decision based on the best data available.