Biphenotypic Philadelphia positive, monosomy seven acute leukaemia: ultrastructural immunocytochemical study.

A case of Ph1 positive acute leukaemia is presented in which an additional chromosome change, monosomy 7 was found. There was no clinical evidence of a pre-existing chronic myeloid leukaemia. Cytochemistry and immunology showed a predominant HLA-DR+, TdT+, cALL- phenotype, with a small percentage of HLA-DR+, Leu-Ml+ and cALL- cells. The true biphenotypic nature of this case was clearly shown by transmission electron microscopy using the immunogold method combined with myeloperoxidase (MPO). Two distinct phenotypes, lymphoid (cALL+, MPO-) and myeloid (LeuMl+, MPO+) were identified with this technique. An immuno-scanning electron microscope technique was also used to study this case, which demonstrated the presence of two different surface morphologies.