Hybrid lymphoid blast crisis of chronic myeloid leukemia with both immunoglobulin and T-cell receptor gene rearrangements

A case of Ph1⁺ chronic myeloid leukemia in blast crisis (CML-BC) is reported, in which the periodic acid Schiff and myeloperoxidase negative blasts displayed high terminal deoxynucleotidyl activity and coexpressed both B- (CD19, CD10, and CD24) and T- (CD7) lymphoid markers. In line with the immunophenotype, DNA analysis revealed a rearranged configuration of both the immunoglobulin and T-cell receptor (beta, gamma, and delta) genes. In spite of this dual B/T phenotype and genotype, the negativity of CyCD3 favors the suggestion that the target of the neoplastic event is an early B cell, with a cross lineage involvement of the putative common recombinase. However, taking into account that a normal counterpart of a biphenotypic B/T ALL has been recognized, it could be hypothesized that the leukemic transformation may have involved an oligopotent B/T lymphoid precursor. This case confirms the lineage heterogeneity of CML-BC and suggests that DNA analyses coupled to extensive immunophenotyping may allow further insight for a more precise recognition of both normal and leukemic ontogenesis.