Abstract
INTRODUCTION: Ado-trastuzumab emtansine (T-DM1) is employed in the treatment of patients with HER2-positive breast cancer. The most common side effects are fatigue, diarrhoea, anaemia, transaminase elevation and drug-induced thrombocytopenia. This report describes a patient with metastatic breast cancer who developed drug-induced lupus due to T-DM1. CASE REPORT: A 54-year-old woman was diagnosed with breast cancer in March 2018. She underwent modified radical mastectomy and axillary lymph node dissection (pT2N1aM0). Following supraclavicular lymph node metastasis in May 2018, she received 8 cycles of docetaxel, trastuzumab, and pertuzumab. In December 2020, the patient presented with axillary and intra-abdominal lymph node metastases, along with bone metastases observed on PET/CT scan. Treatment with T-DM1 and zoledronic acid was initiated. After 18 months on T-DM1, she developed drug-induced lupus. Her symptoms resolved with hydroxychloroquine treatment and discontinuation of T-DM1. DISCUSSION: Drug-induced lupus is a clinical syndrome that shares similar features with systemic lupus erythematosus (SLE). The majority of patients present with symptoms such as arthralgia and myalgia. Hydralazine and procainamide are high-risk drugs for drug-induced lupus. Symptoms usually develop after months or years of use, but may also develop suddenly. Our patient also received TDM-1 treatment for 18 months. We present a case of TDM-1-associated drug-induced lupus in a patient with metastatic breast cancer. This is the first case of TDM-1-related drug-induced lupus reported in the literature.