T cell ALL is a unique separate ALL entity composed of different immunophenotypic and biologic subsets: thymic (CD1a +), mature (surface CD3 +), early (both negative) and its subcategory of early T cell precursor-ALL (ETP-ALL; myeloid markers positive, CD1a negative, CD8 negative, CD5 < 75%). This evidence concerns the gene CD5 and acute lymphoblastic leukemia.