WGS, DuplexSeq and NanoSeq genomic data from histologically normal tissue in cancer patients

The extent to which mutagenic and non-mutagenic processes, including cancer treatment, contribute to somatic evolution in histologically normal tissue remains unclear. We subjected 168 cancer-free normal samples representing 16 different organs from 22 patients with metastatic cancer enrolled in the PEACE research autopsy study to high-depth duplex panel sequencing (coverage >20,000x). In every sample we identified somatic mutations (range 170 - 2,978) at exceedingly low variant allele frequencies (median VAF 0.0000323), consistent with a patchwork of mutated cells in normal tissue. By analysing the mutational spectra of each sample, we extracted 16 distinct single base substitution mutational signatures, reflecting somatic mutational processes that have moulded the genomes of normal cells. Signatures were found to be associated with diverse aetiologies, including alcohol-related mutation acquisition in liver tissue, smoking-induced mutagenesis in lung and cardiac tissue, and multiple distinct treatment-induced processes, which correlated with treatment and its duration. On average, in this cohort in which patients had each received several lines of anti-cancer therapy, exogenous sources, including treatment-related mutagenesis, underpinned >40% of mutations in liver samples, yet <10% in brain samples. Finally, we observed clear differences in the extent and effects of selection in different tissues, with positive selection in certain tissues, including lung (TP53, EGFR and PIK3CA), liver (NF2L2) and spleen (BRAF, NOTCH2), and limited selection in others, such as brain and cardiac. Over 25% of driver mutations in normal tissue exposed to systemic anti-cancer therapy, including mutations in TP53, could be attributed to treatment-induced mutagenesis. Immunotherapy, while not associated with mutagenesis, was linked to an excess of driver mutations in PPM1D and TP53, illustrating how non-mutagenic treatment can sculpt somatic evolution. Our study reveals the rich tapestry of mutational processes and driver mutations in cancer-free normal tissue, and the profound impact of cancer therapeutic and life-time environmental exposures on normal tissue somatic evolution.

• Type: Other
• Archiver: European Genome-phenome Archive (EGA)