PROGESTINS IN HORMONE REPLACEMENT THERAPY: IMPACT ON ENDOMETRIAL AND BREAST CANCER.

Unopposed estrogen replacement therapy (ERT) in non-hysterectomized women creates an unacceptably high risk of endometrial neoplasia that persists even after discontinuation of hormone replacement therapy (HRT). Normally progestin should be given in addition to ERT unless a contraindication to progestin exists: in this circumstance, endometrial surveillance is essential. Continuous combined progestin-estrogen therapy (PERT) appears to offer the greatest protection from endometrial cancer. Accumulated evidence now suggests that ERT has minimal impact on breast cancer risk, especially when compared to other known or suspected breast cancer risk factors. Women developing breast cancer while on ERT have improved survival compared to non-ERT users. Recent reports suggesting an increased breast cancer risk with PERT are based on limited data sets, and are reminiscent of early alarming reports about ERT, which have been largely refuted as larger data sets have become available. Further studies are required to clarify the true impact of PERT on breast cancer and breast cancer mortality.