When assessing the HER2-positive and HER2-negative components separately, we noted that in 10 out of 12 of the HER2 heterogeneous breast cancers the ER status and histologic grade were identical between the two components of a given case, as was the TP53 status in all cases (Figure 1A; Additional file 1). The gene discussed is ERBB2; the disease is breast carcinoma.