EVIDENCE FOR CLONAL EVOLUTION IN PRE-B-CELL LEUKEMIA

This case study provides evidence for clonal evolution in pre-B-cell leukemia. At diagnosis, the lymphoblasts from a 3-yr-old boy were morphologically subtyped as L1 (French-American-British classification). Their immunophenotype was CALLA+ [common acute lymphoblastic leukemia antigen], CIgM+, S[surface]Ig-, TdT+ [terminal deoxynucleatidase], and the karyotype was pseudodiploid with a 1:19 translocation. Striking shifts were apparent when the child relapsed 16 mo. later. Morphologic subtype had changed to L3, CALLA and TdT had disappeared and a consistent karyotype was lacking. Modal chromosome number had increased through clonal evolution to 85, the 1:19 translocation was retained and a new marker, a 14q+ (partial duplication), appeared and was present in a majority of cells. These cytogenetic findings are characteristic of a transforming state. Despite the loss of TdT, the appearance of classic L3 morphology and the acquisition of a 14q+ marker, the cells retained a predominantly pre-B phenotype.