Philadelphia chromosome‐positive mature B‐cell (Burkitt cell) leukaemia

Philadelphia chromosome‐positive (Ph+) acute leukaemia usually shows lymphoblastic morphology and a B‐precursor phenotype. The bone marrow aspirate of a 9‐year‐old boy showed a L3 blast cell morphology in 90% of cells; immunophenotyping revealed a mature B‐blast population. The translocation t(9;22) (q34;q11) was seen in 45 out of 50 metaphases, and expression of the corresponding bcr1/abl fusion transcripts, but no IgH/myc co‐localization or splitting of c‐myc, was demonstrated. Chemotherapy according to the Berlin–Frankfurt–Munster non‐Hodgkin's lymphoma (NHL‐BFM 95) protocol with maintenance according to the BFM acute lymphoblastic leukaemia (ALL‐BFM 90) protocol resulted in continuing complete remission of 54 months. The occurrence of Ph+ Burkitt's leukaemia might reflect multiple‐step cancer development.