CD5 and acute lymphoblastic leukemia: ETP-ALL is a T-ALL subtype characterised by the abnormal expression of stem cell or early progenitor and myeloid markers and the reduced or absent expression of common T cell markers, including CD4, CD8, CD1a, and CD5 (Table 1).75 This immunophenotype signature distinguishes ETP-ALL from all other T-ALL subtypes, including early T-ALL (pro- and pre-), late cortical T-ALL, and mature T-ALL (non-ETP-ALL).