Abstract 808: Functional evaluation of novel germline DNA repair variants identified in patients with early-onset renal cancer

Background: Early-onset renal cancer (eoRC) is typically associated with significant family history of cancer, and often associated with germline pathogenic variants (PVs) in ‘RC-specific' genes including VHL, MET, FLCN, TSC1, TSC2, FH, SDH, PTEN and BAP1. However, most eoRC patients lack PVs in RC-specific genes; rather, we recently identified an enrichment of likely PVs in DNA repair genes in eoRC patients. Here, using eoRC patient resources (primary and transformed lymphocytes, lymphocyte DNA, and tumor tissue), we functionally evaluated the DNA repair variants identified in eoRC patients. Methods: We performed whole-exome sequencing (WES) on lymphocyte DNA from 22 patients with genetically undefined eoRC, with extensive family history of RC and/or other cancers, provided by Risk Assessment Program and Genitourinary Group at Fox Chase Cancer Center. Prioritized variants were assessed by structural, biochemical and cellular studies. Results: 70% of patients had rare, heterozygous, missense variants in genes that suppress DNA damage. ~18% of the variants were in DNA polymerase genes (POLD1, POLE, POLH, POLK), which mediate DNA replication-repair. Increased tumor mutation burden (>10 mutations/Mb) was observed in tumors carrying predicted damaging polymerase variants. In functional testing, induction of DNA damage in primary lymphocytes from eoRC patients and matched cancer-free controls (n=20 each) selectively elevated γH2AX foci (indicative of DNA damage) in cells from eoRC patients (P