Minimally differentiated acute myeloid leukemia in Taiwan: predominantly occurs in children less than 3 years and adults between 51 and 70 years

Acute myeloid leukemia (AML) with minimal differentiation was usually refer red to as acute undifferentiated leukemia in the past. With the help of imm unophenotyping, this subtype of leukemia was shown to express myeloid antig ens on the blasts and was designated AML-M0 by FAB Cooperative Study Group in 1991. Among the 423 consecutive newly diagnosed de novo AML at our insti tution, 12 (2.8%) were of M0 subtype. The proportion of M0 in AML was highe r in children than in adults (8.2% vs 1.7%). Four other M0 patients referre d from outside hospitals for immunophenotyping were also included in this s tudy. There were two peaks in age distribution of these 16 patients: less t han 3 years and between 51 and 70 years, respectively. Organomegaly was mor e common in patients with AML-M0 than in those with other subtypes (56.3% v s 29.2%, P = 0.025). The former patients had higher incidences of CD7 and C D34 expression on the leukemic cells than the latter ones (50% vs 16.9%, P = 0.003 and 69.2% vs 37.9%, P = 0.019, respectively). The patients with AML -M0 showed more frequent clonal chromosomal abnormalities in the leukemic c ells than other AML patients (83.3% vs 53.9%, P = 0.039); the same is also true for complex cytogenetic aberrations (50% vs 11.4%, P = 0.004). Adults with AML-M0 showed a lower complete remission (CR) rate and significantly p oorer survival than those with non M0-AML. However there was no significant difference in outcome between the two groups of pediatric patients. In con clusion, AML-M0 is a unique subtype of leukemia that has distinct age distr ibution and shows different clinical and biological characteristics from ot her AML. Adult patients have poor prognosis. Whether pediatric patients had better outcome than adults needs to be clarified in further studies.