No Evidence of Increased Risk of Breast Cancer in Women With Lynch Syndrome Identified by Multigene Panel Testing

PURPOSEPrior estimates of breast cancer risk in women with Lynch syndrome (LS) range from population risk to 18-fold increased risk with reported differences by gene. Here, breast cancer rates were determined in a large cohort of women with pathogenic variants (PVs) in a mismatch repair (MMR) gene detected through multigene panel testing and compared with rates in the US population and women undergoing panel testing.METHODSMMR gene PV carriers were identified among women tested for suspicion of LS or hereditary breast and ovarian cancer (HBOC) who met inclusion criteria. Standardized incidence ratios (SIRs) and 95% CIs of breast cancer were calculated compared with age-matched incidence in the general US female population and with women negative for PVs stratified by the test indication.RESULTSIn total, 0.8% of women (30,362 of 441,966 women) carried MMR gene PVs. PVs in PMS2 (37.5%) and MSH6 (29.3%) were more common than in MLH1 (13.7%) and MSH2/EPCAM (19.4%). Women with PVs in PMS2 and MSH6 were tested more frequently for HBOC, whereas those with PVs in MLH1 and MSH2/EPCAM were tested more frequently for LS. Breast cancer rates in women with LS were lower than those in the general female population (SIR, 0.88; 95% CI, 0.81 to 0.96) and did not differ compared with women with negative panel testing for HBOC (SIR, 0.90; 95% CI, 0.82 to 0.99) or LS (SIR, 1.02; 95% CI, 0.78 to 1.30).CONCLUSIONIn this large cohort of women with LS identified through panel testing, there was no evidence for increased risk of breast cancer compared with the general US population or women undergoing panel testing. These findings support average-risk breast cancer screening in women with LS.