Risk reducing mastectomy in Norwegian BRCA1/2 carriers

Background: Risk reducing mastectomy (RRM) is an option for women with pathogenic germline variants in BRCA1 or BRCA2 (BRCA1/2). This study investigates and compares RRM-uptake among Norwegian BRCA1/2 carriers from 2008 to 2021, temporal trends, and incidence of breast cancer (BC) after surgery. Methods: BRCA1/2 carriers without prior breast or ovarian cancer, tested at Oslo University Hospital between January 1st, 2008 and December 31st, 2021 were included in the study. Data on RRM was obtained from The Norwegian Patient Registry. RRM-uptake, time from genetic testing (GT) to RRM, and RRM-uptake 2- and 5years post-GT was calculated for all carriers, according to gene and age at GT. RRM-uptake was compared for those tested in 2008/2009 versus 2015/2016. BC diagnoses post-RRM was collected from The Cancer Registry of Norway. Results: In total, 1237 BRCA1/2 carriers were included, 679 (54.9 %) BRCA1 and 558 (45.1 %) BRCA2. Six hundred and four (48.8 %) had chosen RRM, 370 (54.5 %) BRCA1 and 234 (42.0 %) BRCA2 (p < 0.001). Mean age at RRM was 40.1 for BRCA1 and 44.6 for BRCA2 (p < 0.001). Mean time from GT to RRM was 2.3 years for BRCA1 and 3 years for BRCA2 (p < 0.001). Women tested in 2015/2016 were 2.6 times more likely to choose RRM compared to those tested in 2008/2009. Two out of the 604 (0.3 %) had developed BC post-RRM. Conclusion: Nearly half of BRCA1/2 carriers had chosen RRM, with increasing uptake since 2008. Compared to BRCA2 carriers, more BRCA1 carriers chose RRM, were operated at a younger age and sooner after GT. Post-RRM BC incidence was low.