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Aberrant T‐cell antigen expression in B lymphoblastic leukaemia

B lymphoblastic leukaemia (B‐ALL) cells are characterized by the expression of various B‐cell antigens. Expression of T/Natural Killer‐cell antigens, however, has rarely been reported in B‐ALL (TAg+ B‐ALL), and the significance of this aberrant antigen expression is unclear. We thus analysed the frequency of TAg+ B‐ALL at our institution and investigated its significance in the context of immunophenotypes, cytogenetic/molecular findings, and prognosis. We reviewed 134 consecutive cases of B‐ALL and found 18 cases (13·4%) of TAg+ B‐ALL. The most common aberrant T‐cell antigens expressed were CD2, CD5, and CD7 at equivalent rates (each in six cases), CD4 (two cases), and CD56 (three cases). Adverse cytogenetic abnormalities were seen in a significantly larger proportion of the TAg+ cases (72·2%) than the TAg− cases (32·2%; P = 0·003). Multivariate Cox‐regression analysis showed that the risk of relapse over time was higher in the TAg+ cases, independent of high risk status (based on age and white blood cell count) and the presence of adverse cytogenetic abnormalities (hazard ratio = 2·256, P = 0·065). These findings suggest that T‐cell antigen expression in B‐ALL may be an independent predictor of poor prognosis, and a useful marker to identify patients at increased risk for relapse and for harbouring adverse cytogenetic abnormalities.