Carriers of the BRCA1 cancer gene had a significantly increased risk of breast cancer if they used hormonal contraception (HC), pooled cohort data showed.

Breast cancer risk increased by 29% in BRCA1 carriers who reported any use of HC during at least one 12-month continuous period. The risk also increased with duration of HC use, but separate analyses showed no increased risk associated with current use within the past year, 1-5 years in the past, 6-10 years before, or more than 10 years.

The analysis showed no evidence of increased breast cancer risk for BRCA2 carriers who used HC, reported Kelly-Anne Phillips, MD, MBBS, of Peter MacCallum Cancer Center in Melbourne, Australia, and co-authors in the Journal of Clinical Oncologyopens in a new tab or window.

"When counseling women, absolute risks are more useful than relative risks," the authors noted in their discussion of the findings. "These absolute risks will be different for different women, so incorporating our findings into risk prediction models such as CanRiskopens in a new tab or window would assist in providing personalized estimates."

"Decisions about use of HC in women at increased risk for BC [breast cancer] due to BRCA1 mutations need to carefully weigh the absolute risks and benefits," they added. "While shorter-term use may result in only small increases, prolonged cumulative use may result in larger increases in absolute BC risk that may not be acceptable to some women."

An individualized approach to patient counseling about breast cancer risk in BRCA1 carriers is advisable, agreed Yara Abdou, MD, of the University of North Carolina and Lineberger Comprehensive Cancer Center in Chapel Hill.

"These results suggest that for BRCA1 mutation carriers, HC use should be approached with caution, particularly for prolonged durations," Abdou told MedPage Today via email. "Clinicians should engage in detailed risk-benefit discussions with BRCA1 carriers considering HC use, emphasizing the potential increased risk of breast cancer."

"For BRCA2 carriers, the lack of a significant association suggests a lower risk; however, the relatively small number of breast cancer cases in this group warrants cautious interpretation."

The observational design of the study limits the ability to establish a causal relationship between HC use and breast cancer in BRCA1 carriers, Abdou noted. Additionally, the median follow-up of 5.9 years for BRCA1 carriers and 5.6 years for BRCA2 carriers might not be long enough to capture the long-term effects of HC use on breast cancer risk.