CD56 in T-cell acute lymphoblastic leukaemia: a malignant transformation of an early myeloid-lymphoid progenitor?

Concerning biological and clinical aspects,T-cell acute lymphoblastic leukemia is now considered to be a heterogeneous disorder. Here we analyze the impact of particular phenotypic patterns on prognosis of 30 cases of T-cell ALL; poor response to induction treatment and short survival were observed in patients who expressed CD56. The antigen profile of these cases suggests a malignant transformation of an early progenitor belonging to both pathways of differentiation, myeloid and lymphoid. We studied 30 consecutive patients diagnosed as having T-lineage ALL between June 1993 and April 2002. Diagnosis was based on FAB morphological criteria by May-Grünwald-Giemsa staining and EGIL 1,2 immunophenotypic criteria by flow cytometry on bone marrow aspirates. Inmunophenotypic analyses were performed according to standard techniques on a FACScan flow cytometer. TCR γδ or αβ. T-lineage was confirmed in keeping with EGIL proposals. Any aberration in surface antigen expression with regard to hypothetical normal T-lineage differentiation scheme was recorded. 3 All patients were given the Spanish PETHEMA 93 4 and PETHEMA 96 5 protocols for ALL. Relapsing patients were included inexperimental protocols. Complete remission (CR) was considered when bone marrow blast cell counts were below 5%. Continous variables were dichotomized according to the more relevant data in medical literature. 6 All statistical analyses were performed using the SPSS software package. Patients clinical and laboratory data are summarized in Table 1. Twenty-four (80%) of 30 patients achieved CR after induction phase;two of them died because of HCST-related toxicity; nine responding patients relapsed and only one of them is alive.The 5-year overall survival (OS) for the entire group and the median DFS duration, 15.2 months (range 6.5-243.9). Concerning response to induction treatment, only leukocyte count higher than 20 x 10 9 /L and CD56 expression were found to be significant adverse factors by univariate analysis. In multivariate analysis, CD56 expression was finally the only independent prognostic factor for achieving CR in this group (p=0.02). Of note, all CD56-positive T-cell ALL cases expressed CD34 (p=0.04). In addition, CD56-positive cases of TALL showed fewer panT markers than did CD56-negative TALL cases(3 ± 1.4 vs. 4.9 ± 1.7 respectively, p=0.04). None of the CD56 positive cases coexpressed CD4. EGIL subtype frequency and white cell count were comparable among CD56 positive and negative cases. The clinical and laboratory data of the CD56 group are detailed in Table 2. Here we found CD56 to be a marker associated with a worse outcome. Our T-cell ALL patients …