Considering both age groups and stage factors among breast cancer subtypes, patients with the HER2+/HR− subtype had the highest SMR of death from heart disease, at a value of 0.83 (95% CI: 0.68–1.00, p < 0.05), followed by TNBC, at 0.78 (95% CI: 0.68–0.89, p < 0.05), and then by HER2−/HR+ and HER2+/HR+, at 0.75 (95% CI: 0.68–0.82, p < 0.05) and 0.71 (95% CI: 0.62–0.82, p < 0.05), respectively (Figure 3c). This evidence concerns the gene ERBB2 and breast carcinoma.