IgA Vasculitis Developing during Trastuzumab Emtansine Therapy for HER2-positive Breast Cancer.

An elderly woman undergoing trastuzumab emtansine (T-DM1) treatment for HER2-positive breast cancer visited our department with purpura, hematuria, proteinuria, and a decreased renal function. A skin biopsy revealed leukocytoclastic vasculitis with immunoglobulin A (IgA) deposition, confirming the diagnosis of IgA vasculitis. Owing to active renal lesions, the patient was treated with prednisolone and cyclophosphamide, which resulted in clinical remission. A renal biopsy performed five months post-treatment revealed persistent mild proliferative glomerulonephritis with fibrotic crescent formation. This case was considered to have T-DM1-associated IgA vasculitis. Although rare, an awareness of the possibility of serious adverse effects associated with drug administration is important.