Some studies have shown that HER2 2 + heterogeneity is more obvious.[18] HER2-negative conversion after neoadjuvant treatment may be related to tumor heterogeneity and drug resistance, suggesting that there is HER2 heterogeneity within the tumor, HER2-positive tumor cells are effective to chemotherapy and targeted treatment, residual HER2-negative tumor cells, or HER2 positive tumor cells are resistant to trastuzumab. The gene discussed is ERBB2; the disease is neoplasm.