Postmenopausal hormone therapy and the risk of breast cancer: a contrary thought.

The most important unanswered question regarding postmenopausal hormone therapy and the risk of breast cancer is whether hormone therapy initiates the growth of new breast cancers or whether the epidemiologic data reflect a hormonal impact on preexisting tumors. In this perspective I review the evidence favoring hormonal effects on preexisting tumors and suggest that exposure to combined estrogen and progestin is beneficial, causing greater differentiation and earlier detection of breast cancers.