ACUTE PROMYELOCYTIC LEUKEMIA TOLUIDINE BLUE SUBTYPE

In the hypergranular group of acute promyelocytic leukemia (APL) a rar e subvariant with basophilic granules, metachromatic for toluidine blu e, is recognizable. To evaluate the incidence as well as the biologica l and clinical significance of this subtype, we studied 53 consecutive untreated patients with APL with morphological, cytochemical, immunol ogical and cytogenetic methods. In 10 cases (19% of the total) granule s stained metachromatically in percentages of promyelocytes ranging fr om 16 to 60. In these cases peroxidase positivity was weaker than in t he classic hypergranular and microgranular M3 and activities of estera ses were usually present; at the ultrastructural level granules contai ned particulate material. Immunophenotypic and cytogenetic characteris tics seemed not to differ from those of other M3 cases. Coagulopathy w as usually life-threatening, notwithstanding the low white cell count, and the median survival was short. Hyperhistaminemia-related symptoms were not observed. Cytochemical, immunologic and cytogenetic findings are useful to differentiate this form from M2 with basophilic differe ntiation and from mast cell leukemia.