Low expression of the myeloid differentiation antigen CD65s, a feature of poorly differentiated AML in older adults: study of 711 patients enrolled in ECOG trials

Abstract

CD65s appears when the progenitor antigen CD34 disappears, suggesting that this sialylated carbohydrate antigen marks a turning point in normal myeloid differentiation. We characterized acute myeloid leukemia (AML) with low CD65s expression (CD65s^low AML) in 711 patients entered on seven Eastern Cooperative Oncology Group AML treatment trials (1986–1999). Of those, 198 (28%) qualified as having CD65s^low AML. Morphologically, CD65s^low AML was more common in FAB subgroups with minimal differentiation, M0/M1 (P=low than CD65s^high AML (P=low myeloblasts, and the more mature myeloid antigens, CD15 and CD11b, were rarely detected (P=low AML patients were significantly older than CD65s^high cases (Plow cases increased with age, from 20% in patients under the age of 50 years to 67% in patients older than 80 years (P55 years of age, CD65s^low AML had a decreased CR rate of 33 vs 44% in CD65s^high AML (P=0.055). Thus, CD65s^low AML represents immunophenotypically undifferentiated disease and occurs predominantly in older adults. Although not statistically significant, the observed association between low CD65s expression and decreased CR rate only in patients over the age of 55 is intriguing.