Progressively Enlarging Cerebellar Hematoma Concurrent with T-DM1 Treatment.

Background: Trastuzumab emtansine, an antibody-drug conjugate commonly abbreviated as T-DM1, is accepted as effective therapy for trastuzumab-resistant metastatic HER2-positive breast cancer. T-DM1 significantly increases progression-free and overall survival when compared with lapatinib plus capecitabine in patients with HER2-positive breast cancer previously treated with trastuzumab and a taxane. Among the common side effects related to T-DM1, thrombocytopenia and mucosal hemorrhage are seen, although they are infrequently judged to be clinically significant.