[Hypocellular acute leukemia]

To establish diagnostic criteria for hypocellular acute leukemia (HL) 32 cases (mean age 67) with 40% or less bone marrow cellularity were analysed and compared with 40 cases of MDS, 27 cases of AML in the elderly (60 > or = ) and 39 cases of AML in the young (60 <). The mean bone marrow cellularity was 30% in HL, 85% in MDS, 87% in elderly AML and 95% in young AML, respectively. Thus hypocellularity was evident in HL. Blast % in bone marrow of HL patients was 17-70% in all nucleated cells including lymphocytes (ANC), 36-93% in non-lymphocytic cells (NLC) and 50% or more in all cases in non-erythroid/non-lymphocytic cells (NENLC). Thus maturation arrest of blast cells was evident in HL, which corresponds to that of overt AML. Out of 20 cases treated with low-dose ara-C 13 cases (65%) achieved complete remission, but most of them relapsed early by manifesting hypocellular bone marrow again. In conclusion HL is a distinct clinical subtype of AML in the elderly, which can be clearly defined by 40% or less cellularity and 30% or more blasts in bone marrow.