Interest of simultaneous ultrastructural characterization of morphology, cytochemistry and immune phenotype in a case of putative hybrid acute leukaemia.

A case of acute leukaemia is reported in which blast cells expressed some B-related antigens (namely the CALLA antigen) and no peroxidase activity at the optical level; however, some mature granular cells contained Auer rods. Simultaneous characterization of ultrastructural morphology, cytochemistry and immune phenotype was performed. There was an apparent mutual exclusion in the expression of myeloperoxidase activity and the CALLA antigen, and a heterogeneity in the CALLA expression among the blastic population. These results disagree with the hypothesis of a true biphenotypic leukaemia and demonstrate a complete heterogeneity between the lymphoblastoid cells and the myeloid ones. The interest of such a simple combined method in a case of putative hybrid acute leukaemia is emphasized.