Kotsopoulos J, et al. - Researchers investigated the link between hormone replacement therapy (HRT) use and BRCA1-associated breast cancer. Among BRCA1 mutation carriers, the risk of breast cancer did not increase by using estrogen after oophorectomy and this should reassure BRCA1 mutation carriers considering preventive surgery that HRT is safe. Possible adverse effects of progesterone-containing HRT, however, warrants further study.

Methods

• With a mean follow-up of 7.6 years, a prospective, longitudinal cohort study was carried out between 1995 and 2017 with BRCA1 and BRCA2 mutation carriers from 80 participating centers in 17 countries.
• The presence of a personal or family history of breast and/or ovarian cancer had led participants to seek genetic testing for a BRCA1 or BRCA2 mutation.
• Eligible participants were carriers of BRCA1 mutation with no personal medical history of cancer who underwent bilateral oophorectomy following enrollment.
• Detailed information on HRT use was obtained via a follow-up questionnaire every 2 years.
• The hazard ratios (HRs) and 95% CIs associated with the initiation of HRT use post-oophorectomy were estimated using a left-truncated Cox proportional hazard analysis.
• Incident breast cancer was the main outcome.

Results

• The observed mean (SD) age of participants was 43.4 (8.5) years, and among these, 92 (10.6%) incident breast cancers were diagnosed.
• HRT use after oophorectomy showed no relation to an increased risk of breast cancer.
• For ever use of any type of HRT, relative to no use, the observed HR was 0.97 (95% CI, 0.62-1.52; P=.89); however, different effects of estrogen alone and combination hormonal therapy were evident.
• Follow-up of 10 years revealed the cumulative incidence of breast cancer among women who used estrogen-alone HRT was 12% vs 22% among women who used estrogen plus progesterone HRT (absolute difference, 10%; log rank P=.04).