Sinusoidal obstruction syndrome post-treatment with trastuzumab emtansine (T-DM1) in advanced breast cancer.

Trastuzumab emtansine (T-DM1) is an antibody-drug conjugate approved for use in the treatment of human epidermal growth factor receptor 2-positive metastatic breast cancer. Here, we present the cases of two patients with metastatic breast cancer who received T-DM1 monotherapy and developed noncirrhotic portal hypertension (NCPH). Patient 1 presented with ruptured gastric varices at 2 years and 5 months after T-DM1 treatment. Patient 2 presented with intrahepatic portal-hepatic venous shunt at 2 years and 6 months and portal-systemic shunt encephalopathy at 4 years and 11 months after T-DM1 treatment. In both the patients, liver biopsies revealed sinusoidal obstruction syndrome (SOS). T-DM1-induced hepatotoxicity can result from SOS. In long-term administration of T-DM1 the unfavorable events associated with chronic liver circulatory disorder due to SOS, such as NCPH, are concerning. © The Japan Society of Clinical Oncology 2019.