T-cell acute lymphoblastic leukemia (T-ALL), which accounts for approximately 15% of childhood ALL and 25% of adult ALL cases 1, is characterized by a profound infiltration of the bone marrow with clonally rearranged T-cell receptor (TCR) 2 lymphoblasts 3 that stain positively for TdT and express CD1a, CD2, CD3, CD5, CD7, and CD8 1. This evidence concerns the gene CD5 and acute lymphoblastic leukemia.