Expression of CD56 defines a distinct subgroup in childhood T‐ALL with inferior outcome. Results of the ALL‐BFM 2000 trial

Summary This study reports the prognostic impact of the expression of the natural killer cell marker CD56 in a large series of risk‐adapted paediatric patients with T cell acute lymphoblastic leukaemia (T‐ALL; n = 493) treated within the ALL‐Berlin‐Frankfurt‐Münster (BFM) 2000 protocol. The immunophenotype was analysed centrally at diagnosis using flow cytometry and correlated with clinical parameters and outcome. CD56 expression was detected in 7·1% and early T‐cell precursor (ETP) phenotype in 6·7% of all T‐ALL patients. The percentage of ETP in the CD56+ T‐ALL cohort was 4‐fold higher than in the whole cohort. CD56+ T‐ALL frequently expressed the progenitor marker CD34 and myeloid antigens CD13 and CD33. The 5‐year event‐free survival (EFS) rates for the European Group for the Immunological classification of Leukaemias/World Health Organization subgroups and the ETP phenotype were not statistically different. By contrast, patients with CD56 expression had a significantly reduced EFS (60 ± 8%) and overall survival (60 ± 8%) at 5 years, with a hazard ratio of 2·46 (P = 0·002) and 2·99 (P