Trastuzumab Emtansine (T-DM1)-Induced Porto-Sinusoidal Vascular Disorder: A Case Report

T-DM1 is used to treat early and advanced HER2-positive breast cancer and has a favorable toxicity profile. Porto-sinusoidal vascular disorder (PSVD) is a rare complication of this treatment, and its pathophysiology is not fully understood. A 43-year-old female patient was diagnosed with locally advanced HER2-overexpressing breast cancer, treated with primary chemotherapy, followed by surgery and adjuvant radiotherapy and trastuzumab. Distant relapse was identified four years later, and T-DM1 was started, leading to a complete response. Given the alterations in liver enzymes and signs of portal hypertension observed in a CT scan, a liver biopsy was performed, revealing lesions compatible with PSVD. PSVD related to T-DM1 was assumed, T-DM1 was suspended, and the patient remained under surveillance. She remained asymptomatic and with no evidence of disease for seven months. T-DM1-related PSVD is a rare complication of T-DM1 treatment that should not be overlooked. Clinical suspicion is essential for diagnosis, and T-DM1 suspension is the only known treatment.