Ultrastructural features of basophil and mast cell granulopoiesis in blastic phase Philadelphia chromosome-positive leukemia.

Ultrastructural and ultracytochemical studies were performed on blood and bone marrow specimens from 18 patients with Philadelphia chromosome-positive blastic leukemia; 7 patients were in blast transformation following a typical history of chronic myelogenous leukemia and 11 patients presented with "acute leukemia." The patients were divided into 2 morphologic groups on the basis of light microscopic and cytochemical observations. In group I, which consisted of 11 patients, the proliferating cells were "lymphoid" in appearance and demonstrated many cytochemical, biochemical, and immunologic features similar to those of the lymphoblasts of non-T, non-B acute lymphoblastic leukemia. In group II, which consisted of 7 patients, the proliferating cells were myeloid in appearance. On the basis of ultrastructural observations, the 11 group I patients were divided into 2 subgroups, A and B. Subgroup IA, consisting of 5 patients, was characterized by blasts that demonstrated no differentiating features. In subgroup IB, consisting of 6 patients, 20-30% of the leukemic cells contained inclusions that resembled leukemic mast cell or basophil granules. The leukemic cells in the 7 group II patients manifested myeloid characteristics by light microscopy and prominent basophil and mast cell granulopoiesis by electron microscopy. Abnormalities of other myeloid cell lines were also observed in both the lymphoid and myeloid groups of patients.