ERBB2 and breast cancer: Hormone receptor positive (HR+)/HER2− tumors are the most common breast cancer subtypes causing symptomatic LM (44%‐71.4%), followed by HR−/HER2− (12.8%‐25.5%), HR+/HER2+ (10%‐18%), and finally HR−/HER2+ (0.3%‐8.5%).10, 12, 13, 14, 15