Lymphoblastic leukemic transformation (lymphoblastic crisis) in myelofibrosis and myeloid metaplasia

Acute lymphoblastic leukemia (ALL) developing in myelofibrosis (MF) and myeloid metaplasia (MM) is reported in two patients. In both cases, the clinical course of the „blastic crisis” was rapidly progressive with little response to chemotherapy. The circulating cells were readily identified as lymphoblasts on the basis of cytology, cytochemistry, immunologic studies, and ultrastructure. In one of the cases, 40% of cells had T‐cell markers and all cells contained paranuclear acid phosphatase. In the second case, cells had a „Burkitt‐like” appearance, contained multiple cytoplasmic vacuoles positive for oil red O, and one‐third of them had B‐cell markers. The development of lymphoblastic crisis in MF and MM occurs rarely, is analogous to blastic transformation in chronic granulocytic leukemia, and supports the hypothesis that myeloproliferative disorders originate from pluripotent hematopoietic stem cells.