Stratified analysis revealed mutation subtype-specific enrichment in distinct treatment subgroups: the E545K variant was more frequent in radiotherapy-treated HR+ BC patients (OR = 2.72; 95% CI, 1.13–6.55; p = 0.022), while the H1047R mutation was enriched in HER2+ BC patients who had undergone radiotherapy (OR = 3.45; 95% CI, 1.47–8.13; p = 0.004; Figure 3, Supplementary Table S2). The gene discussed is ERBB2; the disease is breast cancer.