Menopausal hormone therapy: assessing associations with breast and colorectal cancers by familial risk

Menopausal hormone therapy (MHT) users are at increased breast cancer (BC) risk and decreased colorectal cancer (CRC) risk compared with never users, but these opposing associations might differ by familial risk of BC and CRC. We harmonized data from three cohorts and generated separate BC and CRC familial risk scores (FRS) based on cancer family history. We defined moderate/strong family history as FRS ≥ 0.4, where 0.4 was equivalent to a 50-year-old woman with one parent diagnosed with either cancer at age 55 years. Of 24,486 women, 1,243 and 405 were diagnosed with incident BC and CRC, respectively. For BC, MHT hazard ratios (HRs) were 1.27 (95%CI = 1.11-1.45) for FRSBC