Extramedullary blast crisis in chronic myelogenous leukemia. Demonstration of t‐cell lineage and philadelphia chromosome in a paraspinal tumor

A case of chronic myelogenous leukemia (CML) with penetrance of the Ph¹ molecular alteration into the T‐cell lineage of a paraspinal tumor is reported. The T‐cell nature of the paraspinal tumor was documented by immunochemical study and genotyping. The Philadelphia chromosome was also detected by genotyping in the same tumor cell population. To the authors' knowledge, this is the first case of extramedullary T‐cell blast crisis in CML demonstrated in an extranodal tumor. The clinical significance of detecting extramedullary blast crisis, and the theories for the scarcity of T‐cell transformation in CML are discussed.