MMRDetect analysis using WES data revealed that 29.4% of MMR-altered breast cancers exhibited MMR deficiency (Table S2), a proportion significantly higher than that observed in MMR-wt breast cancers (5/17 vs. 2/676, p < 0.001, Chi Square test) (Table 1), further supporting that somatic MMR alterations led to impaired function of DNA damage repair in cancer cells, particularly the MMR pathway. Here, MRC1 is linked to breast carcinoma.