A New Approach of Acute Lymphoblastic Leukemia Immunophenotypic Classification: 1984–1994 The GEIL Experience

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Abstract
Several classifications of acute lymphoblastic leukemias (ALL) have been proposed as increasing numbers of technologies and reagents allowed to better characterize leukemic tumor cells. The French Groupe d'Etude Immunologique des Leucemies (GEIL) proposes an immunologic classification of ALL derived from this group's initial attempts and on proposals published by others. Its first step is based on a scoring system where individual markers are assigned major, intermediate and minor weights on a scale of respectively 1.5, 1 and 0.5 points. Assignment to a given lineage requires a score of at least 2 in this lineage. Thus are identified the four levels “null”, “pure”, “variant” and “multiphenotypic”, depending on score combinations in the three B, T and myeloid lineages. In a second step, within each of these classes, cell differentiation criteria are applied to further identify 4 subclasses within PreB-ALL (PreBl to PreB4) and 4 within T-ALL (T1 to T4). ALL with only myeloid markers are referred to as MO. This classification was applied to a series of 1014 scorable ALL. Pure ALL represented respectively 72% in children under 16, and 64% in adults, PreB ALL being significantly more frequent in the former (p < 0.01). B-ALL and T-ALL were significantly (p < 0.05) more frequent in adults (respectively 11% and 27%) than in children (7% and 20%). Null and MO ALLs appeared significantly (p < 0.01) more frequent in adults (3.4 and 3.2%) than in children (1 and 0.3%). Assignment to differentiation steps showed a similar partition of PreB-ALLs subgroups in children and adults, except for PreBl ALL accounting for 10% of adult ALL versus 4% of children ALL(p < 0.001). In infants less than 1 year old, this im-munophenotype was also found prevalent (29% of ALL). Truly multiphenotypic ALL accounted for 3.4% of adult ALL, an incidence significantly (p < 0.05) higher than in children (1.5%). Variants accounted for 26% of ALL of both children and adults, and were mostly CD 15+ variants. T+ variant phenotypes accounted for 5.4% of PreB ALLs, and involved 1 T-cell antigen in 96% of the cases. CD15+ variants were significantly more frequent in PreB1 ALL, and in this case often associated with 11q23 anomalies. Myeloid variant ALL were significantly (p < 0.05) associated with the t(9;22) translocation in PreB ALL, and with T1, CD34+ and class 11+ T-ALLs.