This case provides evidence for a phenotypic switch from a characteristic T-ALL into a typical pre-B ALL. A 17 years old boy presented with massive hepatosplenomegaly and a mediastinal mass. The blasts were characterized as L2 type according to the French, American and British (FAB) classification and the staining with acid phosphatase was positive. The immunophenotype was CD2 +, CD5 +, CD7 + and CD10 -. The patient achieved a complete remission but relapsed 4 years later. At relapse, a striking immunological shift was apparent. The blast cells were now morphologically LI subtype and displayed the CD10 +. C{mew} + phenotype but were CD2 -, CD5 -, CD7 -. These findings are consistent with a transformation of the initial clone although the development of a second leukemia in the same patient could not be excluded with complete certainty.
Keywords: Immunophenotyping; acute lymphoblastic leukemia.