PREB1 (CD10(-)) ACUTE LYMPHOBLASTIC-LEUKEMIA - IMMUNOPHENOTYPIC AND GENOMIC CHARACTERISTICS, CLINICAL-FEATURES AND OUTCOME IN 38 ADULTS AND26 CHILDREN

The less differentiated stage (CD10-) of B-lineage acute lymphoblastic leukaemia (ALL) described as preB1-ALL in the GEIL nomenclature; acco unts for less than 10% of ALL. It is classically considered to be asso ciated with translocation (4;11)(q21;q23), and to have a poor prognosi s. We report an extensive immunophenotypic, genomic and clinical study of a series of 64 preB-1 ALL patients, representing 6.3% of a cohort of consecutive ALLs. The engagement of preB I-ALL cells in the B-linea ge was confirmed by their B-lineage score, equal to or higher than 2. In addition, more than 90% of the cases tested showed rearranged IGH g enes. Translocation (4;11) was the most frequent karyotypic anomaly se en, but only accounted for 24% of the preB1-ALL cases tested. Expressi on of the myeloid associated antigen CD 15 was also found with high in cidence in this subset. Clinical and biological features at presentati on showed more significant differences between preB1- and T-ALL than b etween preB1- and preB2-ALL (CD10(+)). However, outcome characteristic s of the 22 children with preB I-ALL confirmed the worse prognosis of this entity.