Differential chemosensitivity in a child with congenital relapsing acute lymphoblastic leukemia.

Described is a case of a boy with congenital acute lymphoblastic leukemia (ALL) with pre-pre-B-ALL immunophenotype, presenting as diarrhea, organomegaly, hyperleucocytosis of 1434 G/L, and tumor lysis syndrome. The lymphoblasts showed low proliferative activity and high in vitro drug sensitivity measured by the MTT assay. An excellent response to therapy was observed, but relapse ocurred 3 months later. On relapse, blasts showed extremely high drug resistance, high expression of P-glycoprotein, and high proliferative activity. The response to therapy was again positive, but a second relapse occurred in 1 month. The MTT assay indicated increasing drug resistance to all drugs. Cytogenetic analysis revealed deletion in 11q23 locus. This unfavorable case shows complex biology and differential drug resistance in congenital leukemia.