Factors associated with HER2 discordance were MBC subtypes HR+/HER2− (OR = 0.45, [95% CI 0.21–0.98], p = 0.044) and HER2+ (OR = 5.73, [95% CI 2.83–11.60], p < 0.001) compared to HR−/HER2− and primary tumour treatments with endocrine therapy (OR = 2.95, [95% CI 1.47–5.91], p = 0.002). Here, ERBB2 is linked to neoplasm.