It was reported the HER2 status of the primary and metastatic lesions was concordant in only 66% of patients and that the rate of molecular subtype conversion from a primary HER2-negative tumor to HER2-positive metastatic breast cancer was 9.7% [7, 8], which suggested that the molecular subtype conversion of the primary breast cancer occurred during disease progression. The gene discussed is ERBB2; the disease is breast cancer.