ETP-ALL accounts for 10–15% of T-ALL cases and is characterized by genetic features similar to those of hematopoietic stem cells and the early T-cell development immunophenotype (cytoplasmic CD3+, CD1a−, CD8−, CD5−/dim) and by some atypical myeloid antigen positivity [41,119]. The gene discussed is CD1A; the disease is acute lymphoblastic leukemia.