The prevalence of germline mutations among patients with solid tumors with genomic alterations identified on tumor testing: Results from a tertiary care academic center molecular tumor board.

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1516 Background: The proportion of germline versus somatic mutations identified on genomic tumor testing of solid malignancies is not well characterized. We compared somatic and germline testing results in patients with breast, ovarian, pancreatic or prostate cancer with a genomic alteration identified on tumor testing. Methods: Retrospective chart review was performed using a tertiary care academic center’s database of somatic tumor testing results obtained via FoundationOne and Guardant testing. Patients with breast, ovarian, pancreatic or prostate cancer who had a genomic alteration identified on tumor testing, including pathogenic and VUS variants, in BRCA1or BRCA2, CHEK2, ATM, BRIP1, RAD51C, RAD51D, PALB2and CDH1and who had also received germline testing were identified. Analysis was performed to assess prevalence of germline results. The association between mutant allele fraction (MAF) and germline mutation status was also assessed. Results: Results: 124 patients with breast, ovarian, pancreatic or prostate cancer were identified who had a genomic alteration of interest also tested for via germline testing. 54 (32.5%) of tumor mutations were also identified on germline testing. Proportion of genomic results that were germline was wide, ranging from 0-85.7% depending on the gene and variant classification (Table). Germline mutations were present in 36.4% of breast, 25% of ovarian, 53.3% of pancreatic, and 20.9% of prostate cancer patients who had a tumor alteration present. Alterations that were found to be concordant in both somatic and germline testing had an average MAF of 0.54, and alterations identified on somatic testing only had an average MAF of 0.30. Conclusions: Our findings suggest that approximately one-third of genomic alterations on tumor testing will be of germline origin. However, concordance rates may be gene and variant dependent. Higher MAF may be associated with germline alteration status, but further evaluation is needed. Thus, while information provided by genomic tumor testing may be suggestive of a correlating germline mutation, no single alteration type or MAF value is reliably predictive. [Table: see text]