Severe thrombocytopenia induced by trastuzumab rechallenge: a case report and literature review

What is known and objective Trastuzumab can significantly prolong the survival of patients with human epidermal growth factor receptor‐2 (HER‐2)‐positive breast cancer. Trastuzumab‐induced thrombocytopenia is a rare adverse effect. There have been no reports of acute, grade 4 thrombocytopenia after weekly trastuzumab therapy. The study reports a case of a breast cancer patient with severe thrombocytopenia due to trastuzumab infusion (8 mg/kg). Moreover, the patient experienced recurrence of severe thrombocytopenia after receiving weekly trastuzumab therapy (4 mg/kg). Case summary A 52‐year‐old woman with HER‐2‐positive breast cancer developed diffuse petechial haemorrhages and ecchymosis on the lower limbs and gingival bleeding within 24 hours of trastuzumab infusion (8 mg/kg). She was confirmed to have severe thrombocytopenia, which quickly recovered after corticosteroid therapy and platelet transfusion. When her platelet count recovered, we attempted weekly trastuzumab therapy (4 mg/kg); however, thrombocytopenia recurred within 24 hours. Thus, we did not attempt further treatment with trastuzumab. What is new and conclusion We are the first to attempt weekly trastuzumab therapy after thrombocytopenia induced by its initial administration. Reducing the trastuzumab dose did not prevent trastuzumab‐induced thrombocytopenia. Unlike other reports with administration of high‐dose corticosteroid, we found that a standard dose of corticosteroid combined with platelet transfusion was effective in treating trastuzumab‐induced thrombocytopenia.