A 52-year-old woman was admitted to the Department of Breast surgery in our hospital in October 2018. The biopsy showed invasive ductal carcinoma of the right breast. Immunohistochemical staining showed: negative for estrogen and progesterone receptors but positive for human epidermal growth factor receptor-2 (3+ positivity, the result of Fluorescence in situ hybridization test was positive), KI-67 35%. She completed 8 cycles of chemotherapy with EC-T regimen (epirubicin 140mg, cyclophosphamide 800mg, sequential docetaxel 140mg) and modified radical mastectomy. During chemotherapy, we did not observe the occurrence grade 3/4 leukopenia, and the platelet count was in the normal range. The patient did not receive any treatment after chemotherapy. Three and a half months later, she was expected to receive radiotherapy. During the period, the platelet count was still in the normal range. On August 1, 2019, after 17 times of radiation exposures, she started the targeted therapy with 8mg/kg loading dose of single trastuzumab (never used heparin). The second day, she developed acicular rash with dense skin all over the body and gingival bleeding (Figure 1). We considered that this may be caused by radiotherapy, so we didn't review the platelet count, just stopped the radiotherapy immediately, therefore, the gingival bleeding and rash persisted. The first blood routine examination was performed on 5th day after trastuzumab treatment, investigation revealed all the indexes were in the normal range, but platelet count of 1000/mm3. After administration of etamsylate、 high-dose corticosteroid pulse therapy and platelet transfusion, the platelets gradually recovered (Figure 2). During this period, a bone marrow biopsy was obtained. It showed low megakaryocytopoiesis and no sign of infiltration by tumor. Blood film showed platelet count decreased significantly. 7 days after corticosteroid therapy, her platelet count was close to normal and she was discharged. Half a month later, the patient continued to receive radiation exposures, trastuzumab was not administered. During this period, platelet count remained stable in the normal range. So we considered the severe thrombocytopenia caused by trastuzumab instead of radiotherapy.
One and a half months after the end of the radiotherapy, we tried to reduce the dose to prevent trastuzumab-induced thrombocytopenia. Because the interval of trastuzumab exceeded the half-life, so she received 4mg/kg weekly trastuzumab monotherapy (Load-dose). One day after the infusion, her platelet count was 35000/mm3, and after etamsylate、 intravenous infusion of high-dose methylprednisolone sodium succinate、 thrombopoietin (TPO) and platelet transfusion therapy, the trend of platelet decline was more stable than before. Two days after the infusion, her platelet count was 16000/mm3. Because of the treatment timely, there was no spontaneous bleeding or rash. Finally, her platelet count recovered to 108000/ mm3 on the 6th day after corticosteroid therapy (Figure 2). Because the patient still had grade 4 thrombocytopenia with low-dose trastuzumab, therefore, she was not treated with trastuzumab again.