Exogenous reproductive hormone use in breast cancer survivors and previvors.

Considerable controversy exists regarding the safety of elective exogenous hormonal exposure among breast cancer survivors and women at high risk of developing the disease (referred to herein as 'previvors'). We performed a qualitative analysis focused on four areas of potential exogenous exposure to hormones among previvors and survivors: hormonal contraception; systemic hormone-replacement therapy (HRT); localized HRT; and hormonal manipulation for fertility preservation or enhancement. Herein, we discuss the available data and present clinical recommendations regarding the safety of hormonal exposure for both previvors and survivors. We found these data to be hampered by small cohort sizes, heterogeneous patient populations, and limited study designs, highlighting a great need to conduct further research with the aim of enabling better-informed patient management.