Ultrastructure and cytogenetics in seven cases of acute promyelocytic leukaemia (APL).

In the seven cases of acute promyelocytic leukaemia (APL) presented here we have studied the ultrastructural and cytogenetic features which are thought to be of particular significance in this disease. On the basis of our findings from the seven cases of APL described in detail, and our unreported results obtained for a large number of myeloid leukaemias other than APL, we conclude the following. Stellate rough endoplasmic reticulum, certain inclusion bodies and Auer rods having a tubular substructure are, if present, probably diagnostic of APL. However, these structures are not always observed in APL. Inflated rough endoplasmic reticulum is highly indicative of APL while slender cytoplasmic projections, convoluted or lobed nuclei and conspicuous bundles of cytoplasmic fibrils are very common in the abnormal promyelocytes of this disease. There is a strong correlation between the presence of conspicuous bundles of cytoplasmic fibrils and convoluted or lobed nuclei. Most of the APL cases showed the characteristic translocation t(15;17) and we could find no ultrastructural difference between the cases with the translocation and the single example of a normal karyotype.