Response of HER2 positive gallbladder adenocarcinoma to trastuzumab emtansine (T-DM1): a case report and literature review.

The incidence of biliary tract carcinoma (BTC) is gradually increasing, particularly in Asia where it is most common. Compared with other tumors, it has a low incidence but high mortality and is detected at an advanced stage. Metastatic BTCs have fewer options for systemic therapy and limited treatment options beyond symptomatic therapy for patients who have progressed on first-line therapy. There is therefore a need to explore a biomarker-guided personalized treatment approach. This report describes the case of a 46-year-old middle-aged man with human epidermal growth factor receptor 2 (HER2)-positive metastatic gallbladder adenocarcinoma who was treated preoperatively with two cycles of gemcitabine, oxaliplatin, lenvatinib, and sintilimab; the best objective response was stable disease. Subsequent next-generation sequencing showed positive HER2 gene mutation and the patient was treated with trastuzumab emtansine in combination with sintilimab. After 2 cycles, the lesion was reduced in size and surgical resection was achieved, and the patient underwent radical cholecystectomy for gallbladder cancer (GBC), with a disease-free survival of 13 months after surgery. This case demonstrates the efficacy of trastuzumab emtansine in the treatment of locally advanced GBC, suggesting that HER2 mutation is important in GBC and that anti-HER2 drug therapy may be an option for the systemic treatment of GBC.