Abstract 4322: The landscape of mitochondrial DNA mutations in human cancer

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Recent sequencing studies have extensively explored the somatic alterations present in the nuclear genomes of human cancers. Although mitochondria in cancer cells have important roles in energy metabolism and survival, the origins and impact of somatic mutations in mitochondrial DNA (mtDNA) are unclear. Here, we provide a comprehensive analysis of somatic alterations in cancer mitochondria from 1,675 genome sequences across 31 tumor types. We identified 1,907 somatic substitutions which were mainly C:G>T:A and T:A>C:G. These mutations exhibited dramatic replicative strand bias, being almost all C>T and A>G on the mitochondrial heavy strand. This strand-asymmetric mitochondrial mutational signature is different from those found in nuclear cancer genomes but is similar to processes shaping human mtDNA sequence over evolutionary time. The number of mtDNA mutations showed considerable heterogeneity across tumor types, being significantly higher in tumors from gastrointestinal and hepatobiliary systems. With respect to selection, observed missense mutations were nearly neutral and often gradually drifted towards homoplasmy over time. In contrast, mutations resulting in protein truncation showed evidence of negative selection and were more frequently heteroplasmic. Our findings indicate that the endogenous mutational mechanism has far greater impact than any other external mutagens in mitochondria, and is fundamentally linked to mtDNA replication. Citation Format: Young Seok Ju, Ludmil Alexandrov, Moritz Gerstung, Inigo Martincorena, ICGC Breast Cancer Group; ICGC Chronic Myeloid Disorders Group; ICGC Prostate Cancer Group, Mike Stratton, Peter J. Campbell. The landscape of mitochondrial DNA mutations in human cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4322. doi:10.1158/1538-7445.AM2014-4322