Signatures of defective DNA repair and replication in early-onset renal cancer patients referred for germline genetic testing.

Early-onset renal cell carcinoma (eoRCC) is typically associated with pathogenic germline variants (PGVs) in RCC familial syndrome genes. However, most eoRCC patients lack PGVs in familial RCC genes and their genetic risk remains undefined. Here, we analyzed biospecimens from 22 eoRCC patients that were seen at our institution for genetic counseling and tested negative for PGVs in RCC familial syndrome genes. We performed whole-exome sequencing (WES) and found enrichment of candidate pathogenic germline variants in DNA repair and replication genes, including multiple DNA polymerases. Induction of DNA damage in peripheral blood monocytes (PBMCs) significantly elevated numbers of {gamma}H2AX foci, a marker of double-stranded breaks, in PBMCs from eoRCC patients versus PBMCs from matched cancer-free controls. Knockdown of candidate PGVs in Caki RCC cells increased {gamma}H2AX foci. Immortalized patient-derived B cells bearing candidate PGVs in DNA polymerase genes (POLD1, POLH, POLE, POLK) had DNA replication defects compared to control cells. Renal tumors carrying these DNA polymerase variants were microsatellite stable but had a high mutational burden. Direct biochemical analysis of the variant Pol {delta} and Pol {eta} polymerases revealed defective enzymatic activities. Together, these results suggest that constitutional defects in DNA repair such as DNA replication repair underlie a subset of eoRCC cases. These findings may provide opportunities for use of the DNA repair targeting agents for eoRCC treatment. Screening patient lymphocytes to identify these defects may provide insight into mechanisms of carcinogenesis in a subset of genetically undefined eoRCCs. Significance StatementScreening for DNA repair variation may provide a more comprehensive risk assessment for eoRCC patients. Evaluation of DNA repair defects may also provide insight into the cancer initiation mechanisms for subsets of eoRCCs and lay the foundation for targeting DNA repair vulnerabilities in eoRCC.