Exogenous hormonal administration (e.g. HRT during postmenopause) slightly increases the risk of cancer. (5)
Breast cancer risk is also mildly increased by some types of premalignant breast diseases, particularly if they are accompanied by epithelial hyperplasia, atypical ductal and lobular hyperplasias are of greatest risk.
An important risk factor is incidence of breast carcinoma in the contralateral breast. (52)