High-level tumour methylation of and is required for homologous recombination deficiency in solid cancers.

In ovarian and breast cancer, promoter methylation of or is a promising biomarker for PARP inhibitor response, as high levels lead to homologous recombination deficiency (HRD). Yet the extent and role of such methylation in other cancers is not clear. This study comprehensively investigated promoter methylation of eight homologous recombination repair genes across 23 solid cancer types.