Some women may benefit from taking tamoxifen citrate for breast cancer prevention if the probability of benefit outweighs that of adverse events. We determined the proportion of women aged 40 to 69 years attending general internal medicine practices who were potentially eligible for tamoxifen chemoprevention and calculated the maximum proportion of breast cancers that could be prevented.
Six hundred five women aged 40 to 69 completed self-administered questionnaires in the waiting rooms of 10 general internal medicine practices in North Carolina in 2001.
Among white women, 9.0% (95% confidence interval [CI], 5.1%-15.2%) in their 40s, 24.0% (95% CI, 18.2%-31.0%) in their 50s, and 53.4% (95% CI, 46.1%-61.3%) in their 60s had a 5-year Gail model estimated breast cancer risk of 1.66% or greater. Among black women, 2.9% (95% CI, 0%-15.0%) in their 40s, 7.1% (95% CI, 1.1%-24.4%) in their 50s, and 13.0% (95% CI, 3.1%-34.3%) in their 60s had a similar risk. When adverse events were considered in white women, 10% or fewer in all age groups were potentially eligible for chemoprevention. The maximum proportion of breast cancers prevented in eligible women was 6.0% to 8.3%.
Small numbers of women in primary care practices are eligible for discussions about chemoprevention; the maximum proportion of breast cancers prevented if eligible women take tamoxifen is also small. Challenges lie in targeting discussions to the most appropriate women and in finding new chemoprevention strategies that have less risk of harms.