ERBB2 and breast cancer: Hormone receptor (HR)–positive, ERBB2 (formerly HER2)–negative tumors were analyzed in 34 studies (45%),5,6,7,8,10,13,15,17,23,25,26,27,30,31,34,35,36,37 while other studies did not restrict the breast cancer subtype in their analysis and included all subtypes (31 studies [41%]).5,9,12,14,16,18,19,22,24,28,29,32,33,38,39,40,41 The least represented subtypes were ERBB2-positive (6 studies [8%]),5,21 HR-positive with ERBB2 status not described (2 studies [3%]),11,20 and triple-negative breast cancer (TNBC) (2 studies [3%]).5