Regulatory Variants in the KRAS 3′UTR and Intron 2 Are Associated with Breast Cancer Susceptibility Through Independent and Combinatorial Effects in a Mexican Population

Background: Breast cancer (BC) is a leading cause of cancer-related mortality worldwide and a major public health concern in Mexico. Regulatory variants in KRAS, particularly within the 3′UTR and intronic regions, may influence gene expression through microRNA binding and transcriptional regulation. Methods: Five regulatory single-nucleotide variants (SNVs) in KRAS (rs12228277, rs1137196, rs8720, rs12587, and rs12245) were genotyped in BC patients and cancer-free controls. Associations were evaluated using odds ratios (ORs) with 95% confidence intervals (CIs), adjusting for age, alcohol, and tobacco use. Multiple testing was corrected using the Benjamini–Hochberg false discovery rate (FDR). Linkage disequilibrium (LD), multilocus combinations, and in silico functional analyses were also performed. Results: Variants rs12228277, rs1137196, rs8720, and rs12245 showed significant genotype-level associations with BC susceptibility, all remaining significant after FDR correction (pFDR < 0.05). No clinicopathological associations remained significant after correction in single-variant analyses. Multilocus analysis identified specific high-risk combinations (e.g., involving rs12228277, rs1137196, and rs8720) associated with increased BC susceptibility. At the nominal level, these combinations showed associations with clinicopathological features, including hormone receptor–positive status (PR and ER), proliferation markers, and Luminal B subtype; however, none remained significant after FDR correction. LD analysis indicated weak linkage among variants. In silico analyses suggested potential regulatory effects on microRNA binding and KRAS expression. Conclusions: Regulatory variants in KRAS are associated with BC susceptibility through independent effects and potential combinatorial patterns. These findings support the relevance of non-coding variation in cancer risk and warrant further functional and replication studies.