HER2-Positive Conversion in a Metastatic Liver Focus in Late Recurrent Breast Cancer

Late recurrence of estrogen receptor (ER) positive breast cancer is common. When tissues from a recurrent or metastatic focus are available, re-evaluation of ER, progesterone receptor (PgR), and human epidermal growth factor receptor 2 (HER2) status is recommended for treatment selection. This case report describes a 59-year-old woman who underwent surgery for left breast cancer, with a histopathological diagnosis of invasive ductal carcinoma (pathological stage T2N1aM0 Stage IIB, ER positive, PgR positive and HER2 negative). A health check-up 16 years after surgery revealed multiple hepatic mass lesions, and the patient was referred to our hospital for tests. Based on computed tomography, intrahepatic bile duct cancer or metastatic hepatic tumors were suspected, and a liver biopsy was performed. The histopathological diagnosis was a poorly differentiated adenocarcinoma (ER negative, PgR negative and HER2 positive), and the distinction from poorly differentiated intrahepatic bile duct cancer was difficult. Fluorodeoxyglucose (FDG)-positron emission tomography revealed FDG accumulation in the patient's bones and soft tissues, in addition to the hepatic tumors. The patterns and finding of metastasis were compatible with breast cancer recurrence, and the patient was diagnosed with postoperative recurrence of left breast cancer. Pertuzumab, trastuzumab, and docetaxel were started, and the therapeutic effect was assessed as a partial response. It was evident that in this case, the expression of hormone receptors and HER2 differed between the primary focus and the recurrence foci, and this contributed to the treatment strategy. Whenever possible, a biopsy should be performed for lesions that are suspected to be distal metastases.