Granular common acute lymphoblastic leukaemia in adults: a morphological study

2 cases of acute lymphoblastic leukaemia characterised by the presence of cytoplasmic inclusions morphologically similar to azurophil granules are described. Azurophil granulation of blasts is one of the cardinal features which differentiate acute myeloid from acute lymphoblastic leukaemia. Although such granulation of lymphoblasts has caused diagnostic confusion in the past, we found that the granules could be distinguished from myeloid azurophil granules both morphologically and by their characteristic cytochemical staining reactions. They were negative for peroxidase/sudan black and chloroacetate esterase, but gave coarse scattered granular positivity for both acid phosphatase and alpha-naphthyl acetate esterase. Both the electron microscopic appearance of the granules and their cytochemical staining reactions suggested that they were lysosomes. Granular ALL does not appear to be associated with any morphological subtype or karyotype; but is strongly associated with the common ALL phenotype. Its prognostic significance remains uncertain. It occurs more frequently than the small number of previous reports might suggest and, given the potential for misdiagnosis, should be more widely recognised.