The immunophenotype in infant acute lymphoblastic leukaemia: correlation with clinical outcome. An Italian multicentre study (AIEOP).

A detailed analysis of immunophenotype of 112 infants aged less than 18 months with acute lymphoblastic leukaemia (ALL) was performed. Patients were divided into three groups on the basis of age at presentation (under 6 months: group 1: 6-12 months: group 2; 13-18 months: group 3). There were three cases of T-ALL (2.6%). The proportion of other subtypes was: common ALL in 59 patients (52.68%), pre-B ALL in 15 patients (13.3%), pre-pre-B ALL in 27 (24.1%) and acute undifferentiated leukaemia (AUL) in eight patients (7.14%). In non-T ALL, positivity to CD10 (corresponding to C-ALL and pre-B ALL) was distributed in the three age groups as follows: 38.88% (group I) 65.38% (group II) and 86.36% (group III). Conversely, immature phenotypes (pre-pre-B and AUL) were found more often in the younger patients of groups I and II, as well as anomalous phenotypes, such as the presence of myeloid antigens (MyAg) and of CD7. Prognostic significance was evaluated as event-free survival (EFS) by statistical analysis. A better outcome in CD10-positive ALL than in CD10-negative ones (48% v. 25% of long-term survivors) was demonstrated in all infants. Similarly, EFS was significantly better in MyAg-negative than in MyAg-positive cases. These results were confirmed also when adjusting for white blood cell count. This allowed the identification of CD10-negative, MyAg-positive ALL, which were relatively more frequent in infants and had a poorer clinical outcome with the current therapies. This study stresses the prognostic relevance of the immunological study in infant leukaemias and its utility in choosing different therapeutic modalities for poor risk phenotypes.