Immunophenotypic analysis of T‐acute lymphoblastic leukemia. A CD 5‐based ETP ‐ ALL perspective of non‐ ETP T‐ ALL

T‐cell antigens [ CD 5, CD 1a, CD 8] define early T‐cell precursor acute lymphoblastic leukemia ( ETP ‐ ALL ). To understand immature T‐ ALL of which ETP ‐ ALL is part, we used these antigens to subcategorize non‐ ETP T‐ ALL for examining expression of myeloid/stem cell antigens (M/S) and clinical features. Using CD 5 (+/−) to start categorization, we studied 69 routinely immunophenotyped patients with T‐ ALL . CD 5 − was a homogenous ( CD 8, CD 1a) − M/S + ETP ‐ ALL group ( n  = 9). CD 5 + cases were ( CD 8, CD 1a) − pre‐T‐ ALL ( n  = 22) or ( CD 8, CD 1a) + ( n  = 38) thymic/cortical T‐ ALL ; M/S + 20/22 (90.91%) in former and 22/38 (57.89%) in latter ( P  = 0.007). ETP ‐ and pre‐T‐ ALL together ( CD 1a − , CD 5 −/+ immature T‐ ALL group) were nearly always M/S + (29/31; 93.55%). In multivariate analysis, only ETP ‐ ALL predicted poor overall survival ( P  = 0.02). We conclude (i) CD 5 negativity in T‐ ALL almost always means ETP ‐ ALL . CD 1a and CD 8 negativity, as much as CD 5, marks immaturity in T‐ ALL , and the CD 5 +/− / CD 1a − / CD 8 − immature T‐ ALL group needs further study to understand the biology of the T‐ ALL –myeloid interface. (ii) ETP ‐ ALL patients may be pre‐T‐ ALL if CD 2 + ; CD 2 + , conversely, CD 5 − / CD 1a − / CD 8 − pre‐T ALL patients are ETP ‐ ALL . (iii) Immunophenotypic workup of T‐ ALL must not omit CD 1a, CD 5, CD 8 and CD 2, and positivity of antigens should preferably be defined as recommended for ETP ‐ ALL , so that this entity can be better evaluated in future studies of immature T‐ ALL , a group to which ETP ‐ ALL belongs. (iv) ETP ‐ ALL has poor prognosis.