Mature B cell acute lymphoblastic leukemia with MLL-AF9 transcripts: three case reports and literature reviews

Abstract Background: Mature B cell acute lymphoblastic leukaemia (BAL) is characterized by ALL-L3 morphology and the presence of surface immunoglobulin (sIgM) light chain restriction. t(8;14)(q24;q32) or its variants related to the MYC rearrangement (MYCr) are usually present in BAL, and BAL is considered the leukaemic phase of Burkitt lymphoma (BL). BAL with MLL rearrangement (MLLr) is rare. Methods: Three children with BAL and MLLr are presented. We also reviewed the context of 24 previously reported cases, and the features, treatment and prognosis were analysed. Results: Three BAL patients with MLLr were reported between January 2017 and November 2019, accounting for 1.37% of the B-ALL population; 24 patients were found in the literature. Thirteen males and 14 females were included, and the average age at diagnosis was 19.5 ± 4.95 months. Renal, CNS and skin involvement were present in 6, 4 and 3 patients, respectively. Twenty-six (96.30%) patients showed non-ALL-L3 morphology; negative or suspicious expression of CD20 was found in 64% of patients. MLLr was reported, but MYCr was not observed. Twenty-five (92.59%) patients achieved complete remission. Prospective event-free survival (pEFS) in patients who received allogeneic haematopoietic stem cell transplantation (allo-HSCT) was higher than that in patients who received chemotherapy (83.33% vs 41.91%). Conclusion: BAL patients with MLLr had unique manifestations, including a younger age at diagnosis and overexpression of CD19; expression of CD20 was rare, and MYCr was undetectable. The patients were sensitive to chemotherapy, but the pEFS was higher in patients undergoing allo-HSCT than in patients undergoing chemotherapy.