CD34-positive acute promyelocytic leukemia is associated with leukocytosis, microgranular/hypogranular morphology, expression of CD2 and bcr3 isoform

Acute promyelocytic leukemia (APL) has a favorable prognosis. Current thera py includes chemotherapy used in combination with all-trans-retinoic acid ( ATRA). Although the differentiating effects of ATRA on promyelocytes have b een well established, in vitro studies have shown that less-differentiated APL blasts (CD34(+)) demonstrate a variable responsiveness to ATRA. To asse ss the clinical relevance of this finding, we analyzed a cohort of 38 patie nts with t(15;17) and/or PML-RAR alpha APL to determine the incidence and l aboratory features of CD34(+) APL. Thirty-two percent (12/38) of cases were CD34(+). There was a difference in WBC at presentation between CD34(+) and CD34(-) cases (34.6 +/- 9.2, mean +/- standard error vs. 5.4 +/- 2.0, P = 0.009). Patients with CD34(+) APL demonstrated a micro/hypogranular phenoty pe (75%) (P = 0.001), co-expression of CD2(+) 183%) (P = 0.001), and the bc r3 isoform (100%) (P = 0.017). In contrast, CD34(-) cases demonstrated hype rgranular morphology (65%), CD2(+) (15%), and the bcr1 isoform (50%). A hig h presenting WBC count (greater than or equal to 10 x 10(9)/L) was associat ed with an inferior overall survival (Log rank = 0.0047). Patients with CD3 4(+) APL demonstrated an incidence of early mortality of 50%. Despite a mar ked correlation between CD34 positivity and increased WBC count, overall su rvival of CD34(+) and CD34(-) cases did not differ significantly in our sma ll cohort. Immunophenotypic analysis for CD34 expression should be included in future large APL trials to determine if detection of CD34(+) blasts rep resents an independent adverse prognostic factor. Am. J. Hematol. 67:34-41, 2001. (C) 2001 Wiley-Liss, Inc.