Salvage genetic testing on buccal swab samples using liquid in situamplification identifies genetic mutations from previous test failures

Background: NCCN guidelines version 2.2019 address BRCA1/2 testing for men with a personal history of prostate cancer limited to Gleason ≥7 and specific family history features. Inherited genetic mutations have been identified in up to 12% of metastatic prostate cancer, primarily in DNA repair genes. Here we report liquid in situ amplification (LISA) technique followed by hereditary testing on buccal swab samples that had previously failed to yield a genetic testing result. Methods: Previously failed buccal swab samples from another CLIA-certified laboratory were re-prepared using LISA. Qubit quantification following LISA revealed goodDNA concentrations even for these poor-quality swab samples ranging from 5 to 70 ng/uL, which is sufficient for next-generation sequencing analysis (NGS). Coding regions of ATM, BRCA1, BRCA2, CHEK2, PALB2, and RAD51D genes were amplified by a panel of specific primer pools followed by massively parallel sequencing for the identification of germline mutations. Minimal sequencing coverage was set as 50X, and pathogenic, likely pathogenic, and variants of unknown significance (VUS) were classified and reported. Results: Buccal swab samples from 29 men with at least intermediate-risk prostate cancer were received as low-yield, low-quality DNA (n=12), pre-cut swabs in preservation solution (n=6), and aged swab samples (n=11). LISA and subsequent NGS testing was able to salvage results for 24/29 (82.8%) (failed samples included 4 aged swab and 1 pre-cut swab). 1 patient had a pathogenic BRCA1 mutation (c.4309delT) and 3 patients had VUS (BRCA1 c.4776C>G, BRCA1 c.1846_1848delTCT, and RAD51D c.268G>A). The remaining 20/29 (69.0%) samples have either benign or likely benign variants. Conclusions: LISA applied to these previously failed samples was able to salvage results for over 80% of cases, including the identification of a pathogenic BRCA1 mutation which led cascade hereditary testing for immediate family members. It also provided confirmation for nearly 70% of cases about the absence of hereditary risk for the genes on the panel. Citation Format: Glen J. Weiss, Andrew Ford, Charmaine Brown, Elizabeth Caver, Matthew Vallejo, Claribel Adeyemi, Forrest Collins, Chen-Hsiung Yeh. Salvage genetic testing on buccal swab samples using liquid in situ amplification identifies genetic mutations from previous test failures [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4227.