Prognosis of uterine corpus cancer after tamoxifen treatment for breast cancer

Tamoxifen increases the risk of uterine corpus cancer. Since only few, mostly small, studies have examined prognosis of uterine corpus cancer following tamoxifen, we conducted a large retrospective cohort study to further investigate this. We examined histopathologic and immunohistochemical characteristics of 332 patients with uterine corpus cancer following breast cancer, according to tamoxifen use. Survival was examined in the same patients combined with 309 patients from a previous study with updated follow-up. Histological review of all cancers was performed. Long-term tamoxifen users showed a higher proportion of non-endometrioid tumors than non-users (32.7% vs. 17.4%, P = 0.004), especially serous adenocarcinomas and carcinosarcomas. An increased proportion of FIGO stage III and IV tumors was also observed (20.0% vs. 11.3%, P = 0.049). Within FIGO stage I, both short-term and long-term tamoxifen users showed a higher proportion of tumors limited to the endometrium than non-users (35.7% vs. 22.9%, P = 0.049 and 0.004 respectively). Uterine corpus cancers in long-term tamoxifen users were more often steroid receptor-negative (ER alpha, PRA and PRB, P = 2 years tamoxifen = 2.4; 95% CI = 1.2-4.6). In conclusion, this large study clearly shows that tamoxifen-associated tumors have less favorable histological features and a worse survival. Our results can be applied when weighing risks and benefits of tamoxifen versus other hormonal agents used in the prevention and treatment of breast cancer