Abstract 798: Comprehensive genomic profiling of tissue and liquid biopsies reveals the landscape of reversion mutations
Authors: Bailey Shannon T. , Li Meijuan , Thornton James , Yang Lei , Cui Chenming , Hartman Mark , Frampton Garrett , Decker Brennan , Vietz Christine 
Published: June 2022

Abstract
Loss of function mutations in homologous recombination (HR) repair genes predispose individuals to cancer due to the genomic instability brought about by the inability to properly repair DNA. These alterations may also identify patients eligible for treatment with poly (ADP-ribose) polymerase (PARP) inhibitors and platinum drugs that exploit synthetic lethality; however, resistance eventually occurs. This resistance is largely the result of reversion mutations, which restore the DNA repair function of mutated HR genes.
We employed a computational approach to identify patients with breast, ovarian, pancreas, or prostate cancer who underwent comprehensive genomic profiling (CGP; Foundation Medicine, Inc.) and had reversion mutations in the BRCA1, BRCA2, PALB2, RAD51C, or RAD51D genes. Reversion mutations were identified in six different categories: 1) missense mutations that occur at the same amino acid position as a deleterious alteration, 2) non-frameshift deletion mutations that encompass a deleterious alteration, 3) frameshift mutations that restore the open reading frame of another frameshift mutation, 4) splice-site mutations that occur at the same exon as a deleterious alteration, 5) copy number losses that remove a deleterious alteration, and 6) intragenic deletions that lead to loss of deleterious mutation.
Using our computational approach, we identified 483 patients who 1,112 reversion mutation pairs in both solid tissue- and liquid biopsy-derived samples. The most frequently observed category was a non-frameshift deletion of a deleterious mutation. Overall, a greater number of reversion mutations were found in liquid biopsy samples. BRCA2 was the most frequently reverted gene followed by BRCA1, PALB2, RAD51D, and RAD51C. BRCA1-mutated samples had up to six reversion mutations, and for BRCA2, we observed as many as 228 putative reversion pairs in one sample. PALB2, RAD51C, and RAD51D had no more than two reversion mutations. We further examined co-occurring alterations and found correlations with genes in multiple signaling pathways including the MYC signaling pathway, which contained more mutations in reversion-positive samples. Lastly, we explored real-world longitudinal data from reversion-positive samples and found that the presence of a reversion mutation was significantly associated with lower overall survival for breast, ovarian, and prostate cancer patients. In summary, we characterized the landscape of reversion mutations in patients who underwent tissue or liquid biopsy-based CGP during clinical cancer treatment. Our data provide a better perspective for the identification and treatment of cancers involving a reversion mechanism.
Citation Format: Shannon T. Bailey, Meijuan Li, James Thornton, Lei Yang, Chenming Cui, Mark Hartman, Garrett Frampton, Brennan Decker, Christine Vietz. Comprehensive genomic profiling of tissue and liquid biopsies reveals the landscape of reversion mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 798.