Since our dataset was largely HR+ HER2− (Table S1), in order to estimate the dual subtype prevalence in the overall BC clinical population, we iteratively created subsets representing expected distributions of clinical subtypes (https://seer.cancer.gov/statfacts/html/breast-subtypes.html) [29] (70% HR+ HER2−, 13% HR+ HER2+, 5% HR−/HER2+ and 12% HR-HER2−) and we detected 4.92% dual subtypes (95% CI 4.91–4.93) (Fig. S2). The gene discussed is ERBB2; the disease is breast cancer.