P8: CHEMOTHERAPY INDUCED IMMUNE THROMBOCYTOPENIA-AN ENTITY TO KEEP IN MIND

Purpose of StudyThrombocytopenia during chemotherapy is not always due to myelosuppression. We report an unusual case of isolated acute thrombocytopenia after oxaliplatin and irinotecan administration. We reviewed 11 reported cases to better understand the nature of the presentation and variability in response to treatment.Case ReportPatient is a 63 year old female with metastatic colon cancer treated with palliative chemotherapy with FOLFOX. Follwing her 14th cycle she had an episode of acute drop in platelet count to 8,000/microliter. Peripheral smear revealed no evidence of thrombotic microangiopathy. She was managed with supportive platelet transfusions with slow recovery of platelet count. Subsequently she was treated with second line chemotherapy with FOLFIRI. Following the first cycle of Irinotecan, she again had a catastrophic drop in platelets from 136,000/microliter to 6,000/microliter within 10 hours. Due to this recurrent episode, a drug mediated thrombocytopenia was suspected and work up was initiated. She was initially treated with dexamethasone without a significant response. Platelet count normalized after 7 days with supportive platelet transfusions.Methods UsedBlood was tested for drug dependent platelet antibodies by Flow Cytometry at the Platelet and Neutrophil Immunology Laboratory at the Blood Center of Wisconsin.Summary of ResultsThe patient's serum showed evidence of drug dependent platelet antibodies to both oxaliplatin and irinotecan.ConclusionsDrug mediated immune thrombocytopenia is not uncommon. Time to severe acute thrombocytopenia and platelet recovery time varied post exposure of the drug. It is unclear whether steroid or IVIG administration had any effect on the platelet recovery time. Recovery from thrombocytopenia was observed in all 11 cases after the discontinuation of the insulting agent. Confirmation of the presence of drug dependent platelet antibodies against the chemotherapeutic agent by flow cytometry essential for diagnosis. This would be the first reported case of acute thrombocytopenia to two different chemotherapeutic agents in the same patient. Whether the reaction is two different mechanisms or if there is a cross reactivity between Oxaliplatin and Irinotecan has yet to be investigated.