Human epidermal growth factor receptor 2 (HER2) positive is a unique molecular subtype of breast cancer (BC) characterized by high malignancy and poor prognosis. Bilateral primary breast cancer (BPBC) harboring HER2 gene amplification is available to be detected among the BC survivors due to the increasing use of anti-HER2 adjuvant therapy. However, owing to the paucity of cases reported, knowledge of treating HER2-positive BPBC patients including the clinical behavior, histopathologic characteristics, anti-HER2 therapeutic response and disease outcome are not fully understood. Here we report a case of its kind receiving nonstandardized treatment during adjuvant stage. Upon tumor recurrence with liver metastasis, she received trastuzumab combined with chemotherapy and reached a PFS of 14.5 months in first-line treatment. While maintained trastuzumab plus carboplatin as second-line treatment progressed promptly, re-treatment of trastuzumab after lapatinib administration in third line can still benefit the patient. The present case report delineates an anti-HER2 path for a particular characterized patient, and also provides new evidence of trastuzumab re-usage after disease progression of prior anti-HER2 therapy.
Keywords: Bilateral breast cancer; Drug resistance; Human epidermal growth factor receptor 2; Targeted therapy; Trastuzumab.