Discordance between germline genetic findings and abnormal tumor immunohistochemistry staining of mismatch repair proteins in individuals with suspected Lynch syndrome.

Background And Aims: Tumor immunohistochemical staining (IHC) of DNA mismatch repair (MMR) proteins is often used to guide germline genetic testing and variant classification for patients with suspected Lynch syndrome. This analysis examined the spectrum of germline findings in a cohort of individuals showing abnormal tumor IHC.

Methods: We assessed individuals with reported abnormal IHC findings and referred for testing with a six-gene syndrome-specific panel (n=703).

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

Purpose: Prior 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.

Methods: MMR gene PV carriers were identified among women tested for suspicion of LS or hereditary breast and ovarian cancer (HBOC) who met inclusion criteria.