The discordance rate of HER2 status in breast cancer has been reported to be 3–16% [10–13], with 12–19% of HER2-positive tumors in the primary site converting to HER2-negative status at the sites of metastasis/recurrence [11, 12] and 7–10% of HER2-negative tumors converting to HER2-positive status [11, 12, 14]. The gene discussed is ERBB2; the disease is breast carcinoma.