ERBB2 and breast cancer: Martin et al. reviewed more than 230,000 breast cancer patients and reported the incidence of brain metastases by cancer subtype as follows: 0.22%, 0.61%, 1.09%, and 0.68% in HR-positive/HER2-negative patients, HR-positive/HER2-positive patients, HER2-type patients, and TNBC patients, respectively.