Advanced cholangiocarcinoma with human epidermal growth factor receptor 2 (HER2) amplification treated with Trastuzumab deruxtecan (T-DXd): A case report.

[RATIONALE] Human epidermal growth factor receptor 2 (HER2)-positive cholangiocarcinoma is a rare disease with a low incidence and high degree of malignancy. Trastuzumab deruxtecan (T-DXd) has been approved for the treatment of HER2-positive breast and gastric cancer. However, it is still in the initial exploration period for HER2-positive cholangiocarcinoma.

[PATIENT CONCERNS] A 57-year-old Han Chinese male patient with recurrent metastatic cholangiocarcinoma who was tested for HER2 expression in surgical specimens in the absence of reliable drug therapy.

[DIAGNOSES] Postoperative pathological examination confirmed a diagnosis of moderately to poorly differentiated adenocarcinoma of the common bile duct.

[INTERVENTIONS] Our case revealed HER2 amplification and effectively received T-DXd as backline therapy.

[OUTCOMES] After approximately 4 months without disease progression, the patient experienced an increase in plasma tumor markers; however, he regained disease control after receiving T-DXd in combination with lenvatinib with a favorable physical status and quality of life.

[LESSONS] Reexamination of tumor tissue samples to identify target mutations is necessary for backline treatment of cholangiocarcinoma. T-DXd is effective in the treatment of HER2 amplification cholangiocarcinoma and is relatively well tolerated after multiple lines of therapy. The combination of multi-target tyrosinase inhibitors is a possible strategy for overcoming resistance in the future.