Hormone replacement therapy (HRT), breast cancer and tumor pathology

Within an average observation period of 5–6 years, several clinical trials reported an increased risk of breast cancer due to hormone replacement therapy (HRT). However, it remains disputable, whether the increased rate of breast cancers detected within the given time frame is indeed due to newly induced tumors and thus constitutes HRT-initiated primary breast cancers. Onco-pathologically speaking it appears more likely that HRT stimulates the growth of already existing small tumor nests which – due to their small size – would otherwise go undiagnosed. The major arguments are:

1.

Cancer research has established that malignant tumors, including breast cancer, need an average of 5–10 years to expand from a single malignant cell to a lesion of 5–10 mm diameter. A time period of only 5 years, as covered by the respective studies, may well be too short to permit the detection of tumors primarily induced by HRT.