Increased expression of myeloid antigen markers in adult acute lymphoblastic leukaemia patients: diagnostic and prognostic implications.

By applying direct immunofluorescence with a dual-staining technique we were able to demonstrate that 20/37 (54%) patients with acute lymphoblastic leukemia (ALL) expressed both lymphoid and myeloid antigens on the same leukaemic cells. CD13 and CD33 myeloid antigens were detected in 18/20 and in 15/20 cases respectively, and both in 13. Molecular studies confirmed that the four patients with T-cell phenotype had molecular rearrangement of T-cell receptor (TcR) beta chain, and 26 ALL patients with 'B-cell' phenotype showed JH rearrangement. Two ALL patients without (ALL/My-) and three with myeloid antigens (ALL/My+) also demonstrated bcr/abl rearrangement. Both groups of patients had similar presenting features such as age, sex, Hb level, white blood cells, platelet counts and cytogenetic features. Complete response was achieved in 16/17 (94%) ALL/My- patients and in 15/18 (83%) ALL/My+ patients (two deaths occurred during induction) with a mean duration of 17 and 16 months respectively and with similar survival and event-free survival curves. Myeloid antigen expression in adult ALL patients may occur more frequently than previously reported. The presence of myeloid antigen does not identify, in our series, a higher-risk subgroup of patients, although lack of any statistical evidence of prognostic significance needs to be confirmed in a larger case study.