IN-VIVO CLONAL EVOLUTION OF PRE-B TO B-CELL ACUTE LYMPHOBLASTIC-LEUKEMIA IN CHILDHOOD

Two cases are described that provide further evidence for clonal evolu tion in pre-B-cell acute lymphoblastic leukemia. Two infants, whose ly mphoblasts at diagnosis were morphologically subtyped as L1 and immuno phenotyped as HLA DR(+), CD19(+), CD10(+/-) and C mu(+), were induced and maintained in remission. One child relapsed 6 months after initiat ion of therapy. This time his lymphoblasts had L3 morphology and immun ophenotyping demonstrated the appearance of surface immunoglobulins, T he second child relapsed 18 months after initiation of therapy with a lymphomatous picture. He also had peripheral and bone marrow blasts wi th L3 morphology and surface immunoglobulins. A lymph node biopsy show ed diffuse small non-cleaved lymphoma with a 'starry sky' appearance c ompatible with Burkitt's lymphoma. Only one case with a similar clonal evolution has been reported in the literature, but no surface immunog lobulins were demonstrated. The significance of clonal evolution in th ese cases and its potential practical implications are discussed.