A one year boy was admitted to our hospital because of nasal bleeding in January 1984. Significant physical findings included pallor, petechiae and hepatosplenomegaly. Hemoglobin content was 5.9 g/dl, platelet count was 6,000/μl, white cell was 15,300/μl with 7% blast cells and bone marrow revealed hypocellular with 31.5% blast cells.
The majority of blast cells was characterized by large and homogenous nature with low nuclear cytoplasmic ratio, the nucleus was round or oval in shape with one to three nucleoli and a very fine chromatin pattern, the cytoplasm was light blue in color but contained no azurophilic granules. Cytochemical staining proved to be negative for PAS, POX and α-NBE activity. The serum and urinary lysozyme levels were within normal range. Those morphological and cytochemical findings of blast cells were consistent with L2-type leukemia in FAB classification.
However, surface marker studies and immunofluorescence tests for detection of surface and cytoplasmic immunoglobulins showed that the majority of blast cells was found positive for OKM1, Fcγ-R and OKM5. The blast cells had no NK activity. Moreover, by the three days of culture with PMA, the blast cells adhered to the bottom of the plastic culture dish, spread their own cytoplasm and developed macrophage like morphology with long filamentous pseudopods. These cells turned positive in stain for α-NBE activity (NaF sensitivity), while POX reaction remained negative, which suggested that the blast cells transformed into monocyte/macrophage like nature. Chromosome analysis was performed by the G banding technique after short-term culture with colcemid/ethydium bromide and revealed complex transformation, including three translocation with same breakpoint in 11q13, in addition to trisomy 21.
Though the diagnosis was made as L2-type leukemia according to FAB clssification, immunological and culture studies suggested that his blast cells had monocytic nature.
Multi-combination therapy induced complete remission but three months later, he relapsed and expired in February 1985.
