Genetic Mutations By Next-Generation Sequencing in Childhood Biphenotypic Acute Leukemia

Introduction: Biphenotypic leukemia (BAL) or acute leukemias of ambiguous lineage (ALAL) is an uncommon manifestation of childhood acute leukemia. The aim of this study is to further assess clinicopathological characteristics and genetic mutation of de novo BAL or ALAL.

Materials and Methods: Among 377 patients ≤ 18 years old who were diagnosed with de novo Acute leukemia from 2001 to 2017, 12 patients (3.2%) satisfied the definition of BAL by the European Group for the Immunological Classification of Leukaemias (EGIL) criteria or ALAL by World Health Organization (WHO) criteria. By the EGIL criteria, 11 patients were diagnosed as BAL: B-cell/myeloid (B/My) phenotype, 5; T-cell/myeloid (T/My) phenotype, 5. By the 2008 WHO criteria, 7 patients (1.9%) remained as ALAL: acute undifferentiated leukemia (AUL), 2; MPAL, 5. The remaining 5 BAL patients were redirected as ALL (n=3) and AML (n=2). Except one case with ALL by WHO criteria, 11 cases were examined by next generation sequencing using 60 gene panels.

Results: In 5 patients with MPAL by the WHO criteria, a total of 31 distinct mutations were identified in 26 different genes. One case had BCR-ABL gene rearrangement. PTPN11 and NDS1 were recurrent mutation in 2 patients. In 2 patients with AUL, a total of 8 distinct mutations were identified in 8 different genes. In 2 cass of AML, 19 distinct mutations were identified in 15 differnet genes. FLT3-ITD was recurrent mutation. In 2 case of ALL, 17 distinct mutations were identified in 14 differrent genes. The median age of the patients at diagnosis was 8.6 years (range, 0 months-17.8 years). Six patients initially received AML-directed induction therapy, whereas 6 patients received ALL-directed induction therapy. Overall, 7 of the 12 (58.3%) patients achieved a complete remission (CR) after their initial induction therapy. ALL-directed induction chemotherapy was associated with higher chances of achieving a CR as compared to AML-directed regimens (100.0% vs. 16.7%; P =0.015). Nine patients except three cases (1, progression of disease; 1, intracranial hemorrhage during chemotherapy; 1, in continuous CR over 7 years chemotherpay only) underwent an allogeneic hematopoietic stem cell transplantation. With a median follow-up of 5 years, 5 year overall survival (OS) rate was 51.1±15.8% and event-free survival (EFS) rate was 51.9±15.7%. MPAL by WHO criteria seemed to have a better OS and EFS than AUL (both for 75.0 ± 21.7% vs. 0.0%; P=0.008).

Conclusions: BAL or ALAL contains heterogeneous genetic mutation. ALL-directed induction chemotherapy was much better in achieving CR than AML-directed induction chemotherapy. And, patients with MPAL as defined by 2008 WHO definition have better clinical contcome compared with patients with AUL.