Effect of low-dose tamoxifen on benign gynecological and breast conditions in a phase III trial in non-invasive breast cancer

Despite the proven efficacy of tamoxifen (T) in breast cancer prevention, its uptake remains limited due to concerns over side effects. A phase III trial showed that low-dose T (5 mg/day for 3 years) significantly reduces recurrence with minimal toxicity. After 10 years of follow-up, we observed no significant differences in benign gynecological or breast events between the tamoxifen and placebo (P) arms. The uterus was the most frequently affected site (30 cases per arm), followed by the breast (18) and ovary (5 vs 3 on T and P, respectively). Endometrial polyps were similarly distributed. Endometrial thickness remained stable in premenopausal women and showed only a mild, non-clinically significant increase in postmenopausal women on T (∼1.5 mm). Compared with data on standard-dose tamoxifen, rates of benign events were lower. These findings reinforce the favorable safety profile of low-dose tamoxifen. ClinicalTrials.gov: NCT01357772.