Clinical Feature and Genetic Alterations in Myeloid/Natural Killer (NK) Cell Precursor Acute Leukemia and Myeloid/NK Cell Acute Leukemia

Introduction: Myeloid/Natural killer cell precursor acute leukemia (MNKPL) and myeloid/NK cell acute leukemia (MNKL) is a rare hematologic malignancy prevalent in East Asia. MNKPL is characterized by marked extramedullary involvement, immature lymphoblastoid morphology without myeloperoxidase (MPO) reactivity, a CD7⁺/CD33⁺/CD34⁺/CD16⁻/CD15^−/+/HLA-DR⁺ phenotype, myeloid chemosensitivity, and a poor prognosis. By contrast, MNKL shows no extramedullary involvement, a HLA‐DR⁻/CD33⁺/CD16⁻/CD34^−/+ phenotype, myeloid chemosensitivity, and a good prognosis. However, analysis of outcome and genetic alterations in these leukemias are limited. Here, we report outcome and genetic alterations in the patients with MNKPL and MNKL.

Methods: The Leukemia and Lymphoma Committee of the Japanese Society of Pediatric Hematology and Oncology (JSPHO) sent out two questionnaires to 110 JSPHO affiliated hospitals. The first questionnaire requested details of the number of pediatric patients with MNKPL or MNKL had been diagnosed during the period 2000-2013. The second questionnaire requested more detailed information about clinical curses. Overall survival (OS) and event free survival (EFS) defined as relapse or death was analyzed. The protocol of this retrospective study was approved by the review boards of JSPHO and Ehime Prefectural Central Hospital.

We also performed whole exome sequence (WES) using 7 children's samples (5 MNKPL, 2 MNKL) and target sequence using 2 adult's samples (2 MNKPL) from this and another independent cohort. The research protocol was approved by the review board of TMDU.

Results: Thirteen children with MNKPL and 6 children with MNKL were identified. Median age of MNKPL was 8 year-old (range; 0.5-17) and median age of MNKL was 10 year-old (range; 2-13). There are 8 males and 5 females in MNKPL and 4 males and 2 females in MNKL. In MNKPL, central nervous system, mediastinum and lymph node involvement was observed in 1 case respectively. Nasal sinus involvement was observed in 1 case in MNKL. Eleven patients with MNKPL and 3 patients with MNKL were treated with acute myeloid leukemia style chemotherapy and 1 MNKPL patients and 3 MNKL patients were treated with acute lymphoblastic leukemia/non-Hodgkin lymphoma style chemotherapy. Complete remission after induction therapy was achieved in 8/13 MNKPL children and 4/6 MNKL children. Twelve out of 13 MNKPL children and all 6 MNKL children underwent hematopoietic cell transplantation (HCT) with myeloablative conditioning regimen. Median follow up period was 5.3 years in MNKPL and 3.8 years in MNKL patients. 5-year OS of MNKPL and MNKL was 67.3 % and 41.7 %, 5-year EFS of MNKPL and MNKL was 52.7 % and 41.7 % respectively.

In genetic analysis, average 148 somatic mutations in MNKPL and 88 somatic mutations in MNKL were identified by WES. In combined analysis using adult cases, the recurrent mutations were observed in NOTCH1, NRAS (n=3, respectively), MAML2, MAP3K1, SIRPA (n=2, respectively) as activating signal genes, and CLTCL1 (n=2) as cell adhesion molecules, and RECQL4 (n=2) as cell cycle/DNA repair molecules, and PRDM2, CREBBP, SETBP1 (n=2, respectively) as epigenetic modifiers, and WT1, ZNF384, BCLAF1 (n=2, respectively) as transcription factors.

Conclusions: Previously, it has been reported that outcome of MNKL is relatively good than MNKPL. MNKPL and MNKL children had a poor prognosis in our cohort even though most patients received HCT. We identified alteration of molecules involved in NOTCH signaling and RAS-MAPK pathways. In addition, mutations of several transcription factors such as WT1 were identified. The drugs targeting RAS pathway and epigenetic factors may have the potential to improve outcome. An international collaboration for clinical and cytogenetic research of MNKPL and MNKL is needed as they are complex and rare diseases.