Biphenotypic leukemia with unusual chromosomal translocation in a patient treated for melanoma

A patient in complete remission from malignant melanoma but with refractory anemia after nitrosourea treatment developed acute biphenotypic leukemia. This disease, progression was accompanied by expansion of a cytogenetically abnormal clone. At first cytogenetic analysis, 1 year post discontinuation of chemotherapy, only 25% of the metaphases examined were hypodiploid with monosomy 7. Six months later, all of the metaphases seen were 45,XY,-7. Six months before overt acute leukemia was diagnosed, an additional chromosome abnormality emerged, t(2;3)(q31;q27). Although the translocation was present in all metaphases examined, the patient progressed into an acute leukemia with two components: one TdT-positive, Ia-positive, and the other TdT-negative, Ia-positive, monocytoid antigen-positive. This mixed leukemia was identified by double fluorescence staining for intranuclear TdT and surface labeling with a monocyte-specific monoclonal antibody.