Sex steroids and cancer

Hormones, particularly estrogens, have been suspected for many years of being carcinogens. Retrospective studies from the mid-1970s indicate that unopposed estrogen replacement therapy increases the risk for endometrial cancer. However, recent reports have failed to incriminate even unopposed estrogens for any significantly increased risk of breast cancer. Added progestogen, in proper duration and dosage, almost completely negates the estrogen-increased risk for adenocarcinoma of the endometrium. There is increasing evidence that progestogen added to estrogen replacement may decrease the risk for carcinoma of the breast in some women.