ERBB2 and breast carcinoma: JIMT‐1, a HER2‐positive breast cancer cell line, was previously reported to overexpress heregulin.24 Consistent with the BT474‐HRG xenograft model, treatment with pertuzumab and patritumab and especially trastuzumab, pertuzumab, and patritumab induced significant tumor regression compared to that in controls, with the maximum effect induced by the triple combination therapy (P < 0.05; Figure 6B).