Cancer mutation patterns reflect not just the initial DNA damage but the DNA repair pathway choices that follow. Different repair systems leave distinct molecular footprints: error-prone processes introduce substitutions and small insertions or deletions, while high-fidelity mechanisms preserve sequence. Large-scale cancer genome analyses by Ludmil B. Alexandrov and Michael R. Stratton at the Wellcome Sanger Institute revealed recurrent mutational signatures that correlate with specific repair failures and exposures, showing how pathway choice shapes the observable mutation spectrum.
Mechanisms linking pathway choice to mutation types
When a double-strand break is processed by homologous recombination, the use of a sister chromatid typically yields accurate repair. Defects in BRCA1 or BRCA2 compromise this route, producing a characteristic pattern of substitutions and rearrangements identified in studies led by Serena Nik-Zainal at the University of Cambridge and by Alexandrov and colleagues at the Wellcome Sanger Institute. By contrast, repair through non-homologous end joining or alternative end-joining is more error-prone and generates small deletions with microhomology. Base damage is handled by base excision repair and nucleotide excision repair; failures in mismatch repair produce microsatellite instability and a high burden of small insertion–deletion events, a relationship established in clinical and molecular work summarized by Stephen J. Elledge at Harvard Medical School. Enzymatic sources of mutation, such as APOBEC cytidine deaminases, generate clustered C-to-T changes, a phenomenon connected to APOBEC biology by Reuben S. Harris at the University of Minnesota.
Clinical and environmental consequences
Understanding which pathway dominated repair helps interpret causes and therapeutic vulnerabilities. Tumors with homologous recombination deficiency show the mutational signature tied to BRCA loss and are sensitive to PARP inhibitors, a principle advanced by Brian Ashworth at the Institute of Cancer Research. Environmental factors such as ultraviolet light or tobacco create lesion types that bias repair pathway engagement, so regional, occupational, and cultural exposures shape local cancer spectra. At a population level, analyses from The Cancer Genome Atlas at the National Cancer Institute and National Human Genome Research Institute and the International Cancer Genome Consortium link repair-associated signatures to cancer subtype, prognosis, and response to immunotherapy.
Nuance matters: pathway choice is dynamic, influenced by cell cycle stage, chromatin context, and tumor evolution, so mutational spectra reflect both historical exposures and evolving repair competency. Interpreting these patterns requires integrating molecular genetics, epidemiology, and clinical data to translate signature analysis into actionable medicine.