Pathogenic variant detection rate varies considerably in male breast cancer families and sporadic cases: minimal additional contribution beyond BRCA2, BRCA1 and CHEK2

Background Male breast cancer (MBC) affects around 1 in 1000 men and is known to have a higher underlying component of high and moderate risk gene pathogenic variants (PVs) than female breast cancer, particularly in BRCA2 . However, most studies only report overall detection rates without assessing detailed family history. Methods We reviewed germline testing in 204 families including at least one MBC for BRCA1 , BRCA2 , CHEK2 c.1100DelC and an extended panel in 93 of these families. Individuals had MBC (n=118), female breast cancer (FBC)(n=80), ovarian cancer (n=3) or prostate cancer-(n=3). Prior probability of having a BRCA1/2 PV was assessed using the Manchester Scoring System (MSS). Results In the 204 families, BRCA2 was the major contributor, with 51 (25%) having PVs, followed by BRCA1 and CHEK2, with five each (2.45%) but no additional PVs identified, including in families with high genetic likelihood on MSS. Detection rates were 85.7% (12/14) in MSS ≥40 and 65.5% with MSS 30–39 but only 12.8% (6/47) for sporadic breast cancer. PV rates were low and divided equally between BRCA1/2 and CHEK2. Conclusion As expected, BRCA2 PVs predominate in MBC families with rates 10-fold those in CHEK2 and BRCA1 . The MSS is an effective tool in assessing the likelihood of BRCA1/2 PVs.