Hormone replacement therapy use and variations in the risk of breast cancer

Abstract

The risk of breast cancer varies with the formulation and preparation of HRT. Opposed estrogens (progesterone-estrogen) in oral form are associated with an increased risk of breast cancer, which increases with use. Transdermal opposed estrogens, unopposed estrogens and tibolone do not increase this risk. However, this study is an observational study that carries risks of various biases, and thus the findings need to be interpreted with caution.