Trastuzumab emtansine (Kadcyla®) 衛生福利部核准適應症為單獨使用時能夠治療人類表皮生長因子受體 (human epidermal growth factor receptor 2, HER2) 陽性、之前分別接受過trastuzumab 與一種taxane 藥物治療或其合併療法的轉移性乳癌病患。常見副作用有噁心、疲倦、肌痛及肝臟酵素上升等。本文探討一位48 歲女性，診斷為右側乳癌，使用trastuzumab emtansine 治療後因腹脹、呼吸急促等症狀就醫，理學檢查發現病人出現肝功能異常的狀況 (AST = 3,052 U/L, ALT = 718 U/L, total bilirubin = 3.93 mg/dL, prothrombin time = 18 s)，排除病毒性肝炎及併用藥物的因素，懷疑是trastuzumab emtansine 引起的肝臟毒性。根據文獻，trastuzumab emtansine 可能會引發肝毒性（發生率 < 1%）、肝臟酵素上升（grade 4, 發生率 < 1%）。Trastuzumab emtansine 經由與表現HER2 受體的肝臟細胞結合後進入肝臟細胞，進而停止細胞週期並導致細胞凋亡而造成肝臟損傷。臨床上在開始接受治療時需先監測病人肝功能，若病人肝功能異常，應調整劑量或停用，以避免更嚴重的肝毒性發生，確保病人用藥安全。

Trastuzumab emtansine (Kadcyla®) is indicate for use as a single-agent therapy of patients with metastatic human epidermal growth factor 2 (HER2)-positive breast cancer who previously received trastuzumab and a taxane. The common adverse effects include nausea, fatigue, musculoskeletal pain, and increased serum levels of transaminases. This article presents a case of a 48-year-old female with a history of cancer in the right breast, who was admitted to our hospital for symptoms of abdominal fullness and shortness of breath after using trastuzumab emtansine. Laboratory data revealed that serum levels of aspartate aminotransferase, alanine aminotransferase, and total bilirubin were 3,052 U/L, 718 U/L, and 3.93 mg/dL, respectively; the prothrombin time was 18 s. Excluding the use of drugs and viral hepatitis, we suspected trastuzumab emtansine-induced hepatotoxicity, as this drug reportedly induces hepatotoxicity (< 1%) and increased the serum levels of transaminases (grade 4, < 1%). It enters liver cells by combining with HER2 receptors expressed on liver cells, after which it halts the cell cycle and induces apoptosis. Before prescribing trastuzumab emtansine, doctor should check patient’s liver function and adjust the dosage in those with abnormal liver function, to prevent severe hepatotoxicity and ensure patient safety.