[Comment] Serum hormone concentrations and individualisation of breast cancer prevention

Breast cancer poses significant challenges in public health and has a considerable impact globally, with approximately 2·3 million new cases and 685 000 deaths worldwide each year.1 Several efforts revolve not only around improving treatment outcomes but also in preventing the development of this disease. Multiple clinical trials have evaluated endocrine therapies for breast cancer prevention. In a 2019 updated meta-analysis of more than 5 million participants for the US Preventive Services Task Force,2 the relative risk reduction with tamoxifen was 0·69 (95% CI 0·59–0·84), with raloxifene was 0·44 (0·24–0·80), and with aromatase inhibitors was 0·45 (0·26–0·70).