The expression of CD56 antigen in acute promyelocytic leukemia (APL) blasts has been associated with short remission duration and extramedullary relapse. We investigated the clinical significance of CD56 expression in a large series of patients with APL treated with all-trans retinoic acid and anthracycline-based regimens. Between 1996 and 2009, 651 APL patients with available data on CD56 expression were included in 3 subsequent trials (PETHEMA LPA96 and LPA99 and PETHEMA/HOVON LPA2005). Seventytwo patients (11%) were CD56+ (expression of CD56 in ≥20% leukemic promyelocytes). CD56+ APL was significantly associated with high white blood cell counts; low albumin levels; BCR3 isoform; and the coexpression of CD2, CD34, CD7, HLA-DR, CD15, and CD117 antigens. For CD56+ APL, the 5-year relapse rate was 22%, compared with a 10% relapse rate for CD56- APL (P = .006). In the multivariate analysis, CD56 expression retained the statistical significance together with the relapse-risk score. CD56+ APLalso showed a greater risk of extramedullary relapse (P < .001). In summary, CD56 expression is associated with the coexpression of immaturity-associated and T-cell antigens and is an independent adverse prognostic factor for relapse in patients with APL treated with all-trans-retinoic acid plus idarubicin - derived regimens. This marker may be considered for implementing riskadapted therapeutic strategies in APL. The LPA2005 trial is registered at as NCT00408278.

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Erasmus MC: University Medical Center Rotterdam

Montesinos, P, Rayón, C, Vellenga, E, Brunet, S, González, J, González, M, … Löwenberg, B. (2011). Clinical significance of CD56 expression in patients with acute promyelocytic leukemia treated with all-trans retinoic acid and anthracycline-based regimens. Blood, 117(6), 1799–1805. doi:10.1182/blood-2010-04-277434