In the age range of 55–74 years, which constituted the largest population in our study, patients with the TNBC breast cancer subtype exhibited the highest SMR, at 0.95 (95% CI: 0.80–1.11), followed by the HER2+/HR− subtype, with an SMR of 0.88 (95% CI: 0.67–1.14). The gene discussed is ERBB2; the disease is breast carcinoma.