BACKGROUND: 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. OBJECTIVE: This study aims to analyze the clinical and biological features of MPAL and to evaluate the therapeutic approaches in children diagnosed with MPAL. METHODS AND SETTINGS: 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. RESULTS: 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%. CONCLUSION: 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.