[An unclassifiable case of hypoplastic leukemia in old age treated successfully with vincristine and prednisolone].

An 80-year-old male was admitted because of dizziness and palpitation. Laboratory investigation revealed pancytopenia. A bone marrow aspirate showed a markedly hypocellular marrow with 41.6% blast cells. Peroxidase activity was negative and PAS reaction was block positive in the blast cells. Surface markers of these cells were positive for HLA-DR antigen and partially positive for CD13 (MY7). Other markers, such as T, B or myeloid antigens were all negative. These blast cells were classified as L1 according to the FAB system but suggested essentially unclassifiable in cell differentiation. The patient was treated successfully with vincristine and prednisolone and induced into complete remission although repeated marrow examination findings revealed hypocellular. As for the classification of hypoplastic leukemia, lymphoid or primitive "stem cell" leukemia also should be considered as other categories of acute leukemias and be treated according to each case.