ERBB2 and breast cancer: We have reported that 18% of HER2-positive breast cancers had HER2 ITH, and other studies have indicated that 11–40% of HER2-positive breast cancers had ITH of HER2 expression within the tumor, which may cause inaccurate HER2 status assessments, potentially affecting therapeutic decision-making [14,15,16,17,18,19,20].