Severe thrombocytopenia induced by a single infusion of trastuzumab.

We report a case of severe thrombocytopenia related to adjuvant trastuzumab use. Less than 24 hours after administration of her first dose of single-agent trastuzumab, the patient was admitted to the hospital with a platelet count of 2 x 10(9)/L. Trastuzumab is being increasingly used and, to our knowledge, severe thrombocytopenia has not yet been reported as an adverse event. This case highlights a serious and potentially life-threatening complication with the use of single-agent trastuzumab.