Estimating the Risks and Benefits of Tamoxifen for Prophylactic Breast Cancer Chemoprevention in Korea

PURPOSE According to the National Surgical Adjuvant Breast and Bowel Project P1 (NSABP-P1) study, tamoxifen can prevent 49% of invasive breast cancers in patients who have a 5-year risk of 1.67% or more. Because tamoxifen is associated with both adverse effects (endometrial cancer, stroke, pulmonary embolism) and protective effect (fracture prevention), it is necessary to weigh the risks and benefits of using tamoxifen for prevention in Korean women. This study weighed those risks and benefits. METHODS Data were reviewed on the incidences of breast cancer, hip fracture, endometrial cancer and stroke in the absence of tamoxifen treatment in Korean women. We also reviewed NSABP-P1 data on the effects of tamoxifen on these outcomes. A risk-benefit index was calculated according to age and specific risk of breast cancer. Sensitivity analyses were performed with assumptions regarding the effects of tamoxifen. RESULTS Compared to U.S. women, the numbers of hip fractures and endometrial cancers were lower, but the number of strokes was much higher. The net benefit of tamoxifen was reduced with increasing age because of a high risk of stroke in older women. Older Korean women had more risk than benefit from tamoxifen chemoprevention. Only women younger than age 40 had a positive risk-benefit index with an average 5-year risk of breast cancer in Korea. Sensitivity analysis showed that this result was robust. CONCLUSION Women under the age 40 had more benefit than risk from tamoxifen chemoprevention. Tamoxifen chemoprevention should be limited to Korean women younger than age 40.