Megan L. Marshall

Supplementary Materials, References, Tables and Figures

Supplementary Materials, References, Tables and Figures

Supplementary Materials, References, Tables and Figures

Supplementary Materials, References, Tables and Figures

Supplementary Materials, References, Tables and Figures

Pathogenic protein-truncating variants of RAD51C, which plays an integral role in promoting DNA damage repair, increase the risk of breast and ovarian cancer. A large number of RAD51C missense variants of uncertain significance (VUS) have been identified, but the effects of the majority of these variants on RAD51C function and cancer predisposition have not been established. Here, analysis of 173 missense variants by a homology-directed repair (HDR) assay in reconstituted RAD51C−/− cells identified 30 nonfunctional (deleterious) variants, including 18 in a hotspot within the ATP-binding region. The deleterious variants conferred sensitivity to cisplatin and olaparib and disrupted formation of RAD51C/XRCC3 and RAD51B/RAD51C/RAD51D/XRCC2 complexes. Computational analysis indicated the deleterious variant effects were consistent with structural effects on ATP-binding to RAD51C. A subset of the variants displayed similar effects on RAD51C activity in reconstituted human RAD51C-depleted cancer cells. Case–control association studies of deleterious variants in women with breast and ovarian cancer and noncancer controls showed associations with moderate breast cancer risk [OR, 3.92; 95% confidence interval (95% CI), 2.18–7.59] and high ovarian cancer risk (OR, 14.8; 95% CI, 7.71–30.36), similar to protein-truncating variants. This functional data supports the clinical classification of inactivating RAD51C missense variants as pathogenic or likely pathogenic, which may improve the clinical management of variant carriers. Significance: Functional analysis of the impact of a large number of missense variants on RAD51C function provides insight into RAD51C activity and information for classification of the cancer relevance of RAD51C variants.

576 Background: Young age at onset is a hallmark feature of an inherited predisposition to cancer. Recent evidence suggests that the incidence of pathogenic/likely pathogenic variants (PV) in cancer predisposition genes among individuals diagnosed with colorectal cancer (CRC) ≤ age 35 is high, but few studies have examined the frequency identified by multi-gene hereditary cancer panel testing. We report on PV yield and clinical presentation of individuals diagnosed with CRC ≤ 35 years (y). Methods: We retrospectively reviewed test requisition forms and provided pathology reports for 4,727 individuals with CRC who underwent panel testing of, at a minimum, MLH1, MSH2, MSH6, PMS2, EPCAM, APC, and MUTYH. Two-tailed Fisher’s exact tests were used to determine statistically significant differences between groups. Results: Of the 691 individuals diagnosed with CRC ≤35y, 137 PV were identified in 126 individuals (126/691, 18.2%), including 72 with Lynch syndrome, 16 with familial adenomatous polyposis (FAP), five with MUTYH-associated polyposis, four with constitutional mismatch repair deficiency, one with juvenile polyposis syndrome, and one with Peutz-Jeghers syndrome. Thirty-eight additional PVs were identified in other non-CRC genes. Microsatellite instability (MSI) and immunohistochemistry (IHC) results were reported for 277 individuals and were reportedly abnormal in 63. The yield of PV in individuals with abnormal tumor studies was 52.4% (33/63); PV in genes other than the Lynch syndrome-associated genes were identified, commonly in the MSI-H group. While statistical significance was not observed, the positive rate was higher for individuals with non-rectal cancers (colon cancer: 104/534, 19.5%; rectal cancer: 22/157, 14.0%, p = 0.13). Conclusions: In our cohort, 18.2% of individuals diagnosed with CRC ≤35y were found to harbor a PV. Yield increased in those with abnormal MSI/IHC as well as non-rectal tumor location. Hereditary predispositions in patients diagnosed with very early-onset CRC are not limited to Lynch syndrome and FAP. Therefore, individuals with very early-onset CRC may benefit from multi-gene panel testing rather than syndromic-based testing.