Kataegis Expression Signature in Breast Cancer Is Associated with Late Onset, Better Prognosis, and Higher HER2 Levels.

Kataegis is a mutational process observed in ∼55% of breast tumors that results in hypermutation in localized genomic regions. Using whole-genome sequence data of 97 tumors, we examined the distribution of kataegis loci, showing that these somatic mutations are over-represented on chromosomes 8, 17, and 22 and enriched in genic regions and active chromatin elements. We show that tumors harboring kataegis are associated with transcriptome-wide expression changes consistent with low invasive potential. We exploit the kataegis expression signature to predict kataegis status in 412 breast cancers with transcriptome but not whole-genome sequence data and show that kataegis loci are enriched in high-grade, HER2(+) tumors in patients diagnosed with breast cancer at an older age and who have a later age at death. Our study demonstrates that kataegis loci are associated with important clinical features in breast cancer and may serve as a marker of good prognosis.