Acute Leukemia of Ambiguous Lineage (ALAL)

Abstract

Ambiguous lineage acute leukemia (ALAL) is a rare subtype of acute leukemia and is defined immunologically. ALAL consists of mixed phenotype acute leukemia (MPAL) and acute undifferentiated leukemia (AUL). MPAL is further divided into subtypes such as B/M MPAL, T/M MPAL, and B/T MPAL. Recently, the genetic basis of MPAL has been revealed as an acquisition of mutations in immature hematopoietic progenitors. There are shared genetic features between B/M MPAL with ZNF384 and B-cell acute lymphoblastic leukemia (ALL) with ZNF384 as well as T/M MPAL and early T-cell precursor ALL. Treatment for ALAL has not been established. However, treatment of ALL-type is significantly more effective than treatment of acute myelogenous leukemia. Generally, the prognosis of pediatric ALAL is worse than that of pediatric ALL. Treatment selection based on the genetic background is recommended. ALAL with genetic features of ALL, such as BCR-ABL or KMT2A alterations, and CD19 positive ALAL should be treated using ALL treatment. Treatment switching, either ALL-type to AML-type or vice versa, is beneficial for few ALAL cases. Hematopoietic stem cell transplantation is indicated for patients with poor efficacy of induction treatment.