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 ؉ APL also 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 http:// www.clinicaltrials.gov as NCT00408278. (Blood. 2011;117(6):1799-1805)
t-MN is a relatively infrequent, long-term, and severe complication after first-line treatment for APL with ATRA and anthracycline-based regimens. Therapeutic strategies to reduce the incidence of t-MN are warranted.
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