Chromosome 20q and 13q gain in metastatic colorectal cancer: Prognostic significance and genomic correlates.

e15553 Background: Chromosome 13q and 20q gain are major molecular events in adenoma-carcinoma progression and metastasis. The prognostic significance and correlates of 13q and 20q gain in metastatic colorectal cancer (CRC) have not been established. Methods: A total of 108 cases were selected at the University of Louisville. We ran a custom research-use only algorithm to assess whole arm chr13q and chr20q gain from next generation sequencing data of CRC samples. The algorithm utilized the coverage data of baited regions of the genome to model the copy number of each segment. A gain call was made if > 50% of the chromosome arm was gained. Tumors were noted as left-sided colon, right-sided colon, or rectal cancers. Data on demographics, treatment and Kaplan-Meier survival were analyzed. Results: The prevalence of 13q gain was 58% and 20q gain was detected in 61% of cases. Concurrent 13q and 20q gains were frequent, with 49% prevalence. The only 2 MSI-High samples were negative for 13q or 20q gain. Tumors with 13q and 20q gain were significantly more likely to have mutations in TP53 and APC (Table). Rectal tumors were significantly enriched for 13q gain ( p= 0.020) and 20q gain ( p= 0.007). Examining survival by tumor location, 13q gain conferred significantly worse outcome for rectal cancers ( p= 0.007), as did 20q gain ( p= 0.037). Conclusions: With median follow up of over 3 years, 13q and 20q gains were significantly associated with worse prognosis in rectal cancers. The data indicate that 13q/20q gain and associated molecular signature are important prognostic markers in CRC.[Table: see text]