First reported case of secondary mixed phenotype acute leukemia after multiple myeloma.

In recent years the outcome of patients with multiple myeloma (MM) has significantly improved, due to new drugs. However, some agents, i.e. the alkylating drug melphalan, can be associated with an increased incidence of secondary malignancies. Myelodysplastic syndromes and acute myeloid leukemia are reported in the literature, and rarely acute lymphoblastic leukemia. Here we describe a unique case of a 56-years old female patient affected by MM since 2015 in complete remission after autologous stem cell transplant and in lenalidomide maintenance, who developed 2 years later mixed phenotype acute leukemia (MPAL). The patient, refractory to both lymphoblastic and myeloid acute leukemia regimens, achieved complete remission with bi-specific anti-CD19/anti-CD3 monoclonal antibody blinatumomab and with hypomethylating agent azacytidine plus the BCL-2 inhibitor venetoclax. She then underwent hematopoietic stem cell transplantation from HLA-identical sibling donor and she is still in complete remission after 9 months. To the best of our knowledge, there are no cases in the literature describing MPAL after autologous transplant for MM. Our patient was treated with blinatumomab and venetoclax and achieved complete remission 9 months from allogeneic transplant. The mechanism underlying the development of MPAL is not completely understood and therapies are still lacking. In this context the combination of blinatumomab, azacytidine and venetoclax successfully used in this patient may provide food for thought for further studies in this rare setting of patients.