Mixed phenotype acute leukemia (MPAL), also known as biphenotypic acute leukemia (BAL), is an uncommon subgroup of leukemia that exhibits features of both lymphoid and myeloid lineages.

This study aims to analyze the clinical and biological features of MPAL and to evaluate the therapeutic approaches in children diagnosed with MPAL.

It was a retrospective study that included children (age<18 years old) diagnosed with MPAL, based on the European Group for Immunological Characterization of Leukemia or the 2008/2016 WHO criteria, in the pediatric hematology department of Aziza Othmana Hospital in Tunisia, from 2006 to 2022.

Of 639 patients with acute leukemia, 10 (1.5%) were diagnosed with MPAL (10 of 639). The median age at diagnosis was 9 years old (range, 4–18 years) with a gender ratio of 1.5. The median initial leukocyte count was 28.3×10⁹/L (range, 1.6–143×10⁹/L). None of the patients had central nervous system involvement. Four patients (40%) had a T/Myeloid phenotype and 6 patients (60%) had a B/Myeloid phenotype. Cytogenetic abnormalities were seen in 7 cases (70%). The BCR-ABL fusion gene was detected in 2 patients (20%). None of the patients had a KMT2A rearrangement. All patients initially received acute lymphoblastic leukemia (ALL) chemotherapy using the EORTC 58951 protocol. Within these patients, one patient (10%) died during the induction phase and 9 (90%) achieved morphologic complete remission at the end of induction. Only one patient underwent allogeneic hematopoietic stem cell transplantation.

Treatment-related mortality was 20% (2 cases). The median follow-up time was 38 months (1–202 months). The 3-year event-free and the 3-year overall survival rates for the entire group were 60%.

MPAL is rare and complex, with heterogeneous clinical and biological features. A literature review suggests that ALL chemotherapy is better for achieving a favorable prognosis than AML regimens.