CD7+ TdT+ chronic myelogenous leukemia blast crisis with null genotype

Chronic myelogenous leukemia (CML) commonly evolves into blast crisis (BC). The blasts are usually of myeloid phenotype (70%), and less commonly of B-lymphoid phenotype (30%). Only rare reports of T lymphoblastic phenotype, and even fewer documented cases of T lymphoblastic genotype, are found. We report a case of Philadelphia (Ph) chromosome containing CML that evolved into a CD7+, TdT+, CD4-, CD8-, CD34-, HLA- DR+, blast crisis. The BC cells contained the Ph chromosome and expressed fusion bcr-abl RNA by polymerase chain reaction analysis, but had germline configuration of the T-cell receptor genes beta and delta, as well as germline configuration of immunoglobulin genes for heavy chain and kappa and lambda light chains. This case of CD7+ TdT+ leukemia thus represents either an early T-cell or true stem cell BC of CML, and demonstrates the need for gene rearrangement studies in T-cell phenotype BC.