Blinatumomab resistant clone presenting as mixed phenotype myeloid sarcoma causing cord compression

Introduction/Objective Blinatumomab is a monoclonal antibody directed against CD19/CD3 utilized for the treatment of relapsed or refractory B-cell precursor acute lymphoblastic leukemia (ALL) and for the treatment of B-cell precursor ALL in first or second complete remission with minimal residual disease (MRD) ≥0.1%. Although Blinatumomab treatment has shown better overall survival, progression-free survival, and complete remission when compared to chemotherapy, most patients have a relapse and ultimately succumb to the disease. Interestingly, there are a number of cases reporting relapse in extramedullary places. The mechanisms for relapse in these unusual extramedullary sites are not well-understood. We herein report a case of a 20-year-old African American male with primary refractory Philadelphia-negative (Ph-) precursor B cell ALL with MLL rearrangement, who received treatment with Blinatumomab after achieving morphological remission with a pediatric-inspired regimen but found to be MRD +. Methods/Case Report A 20 year old African American male was found to have B cell precursor ALL. It was found to be Ph-. While initally receiving vincristine, prednisone, and aspariginase, the ALL proved to be refractory to treatment. Blinatumomab was used as second line therapy after the first failed remission. The patient remained with morphological response; however, remained MRD+ after three cycles of Blinatumomab. During the fourth cycle, the patient presented with back pain and lower extremity weakness. A spine MRI revealed an extradural mass in the thoracic spine causing cord compression. A thoracic laminectomy with partial removal of the mass, followed by radiation, was performed with improvement of symptoms. Pathology results of the extradural mass revealed a myeloid sarcoma with MLL rearrangement. Results (if a Case Study enter NA) NA Conclusion This case report demonstrates how patients treated with blinatumomab can have relapse in unusual extramedullary places. The possibility of leukemia manifesting in extramedullary sites should always be kept in mind by clinicians treating patients with Blinatumomab. The mechanisms of resistance against Blinatumomab are not well- understood and need further elucidation.