Minimally differentiated acute myeloid leukaemia (AML-M0): cytochemical, immunophenotypic and cytogenetic analysis of 19 cases.

We describe our experience in the identification of 19 cases of AML-M0 categorized among 200 consecutive AML cases. Leukaemic cells from our cases were morphologically marked by agranular basophilic cytoplasm, finely dispersed chromatin and prominent nucleoli. In two cases heavily vacuolated and monocytoid-shaped blasts were also observed. Cytochemistry (MPO, SBB, alpha ANAE, alpha NBE, NASDCAE, AP, PAS) was negative in 14 cases, five cases expressing a very faint cytoplasmic positivity for alpha NBE (not exceeding 30% of the blasts) and alpha ANAE (not exceeding 41%) which was sodium fluoride resistant. In these five cases other monocytic markers (e.g. CD14) were not in favour of myelomonocytic differentiation. All the cases were anti-MPO positive at frequency > 10%. Phenotypic analysis also revealed myeloid features with all the patients having at least one myeloid antigen (CD13, CD33, CD15), Tdt was expressed in nine cases and CD7 in six cases. All cases but one were positive for CD34. Cytogenetic analysis, performed in 16 cases, showed no adequate growth in two cases and no consistent abnormality in four; among the remaining 10 cases no consistent abnormality was observed, the most common finding was trisomy 8 (two cases) and 4 (two cases) and aberrations of chromosomes 2, 3, 5, 7, 9, 12 and 21. No cases of (t9;22), Ph chromosome were observed. Interestingly three out of five patients with faint alpha NBE/alpha ANAE positivity relapsed as typical M4 (one case) or M5a (two cases).