EXPRESSION OF CD24 (BA-1) PREDICTS MONOCYTIC LINEAGE IN ACUTE MYELOID-LEUKEMIA

Fifty-seven cases of acute myeloid leukemia (AML), which had been subt yped by French-American-British morphologic and cytochemical criteria as myeloid (M1, M2) or monocytic (M4, M5), were retrieved from the fil es of the Division of Hematopathology, University of Iowa. Correspondi ng immunophenotyping data were reviewed with attention to the expressi on of CD14 (MY4) and CD24 (BA-1). Of 20 cases expressing CD24, 19 were M4 or M5, whereas all 14 cases expressing CD14 were of monocyte linea ge. Therefore, CD14 was a highly specific (100%) but only moderately s ensitive (58%) marker for distinguishing classes M1 or M2 from M4 or M 5. By contrast and unexpectedly, CD24 was nearly as specific (97%), bu t more sensitive (79%) in marking M4 or M5 cells. This appears to be t rue even though CD24 is apparently not expressed on normal monocytes. When positive staining for either or both antibodies (CD24 or CD14) wa s considered indicative of a monocytic leukemia, the sensitivity of im munophenotyping in distinguishing M4/M5 from M1/M2 AML rose to 92%, wh ile maintaining 97% specificity. The authors discuss a recent observat ion that may help explain the unexpected expression of CD24 in monocyt ic AML. They conclude that the usefulness of CD24 in identifying monoc ytic AML may exceed that of CD14, and that the use of CD24 and CD14 in combination improves the ability of flow cytometry to distinguish mye loid from monocytic acute leukemias.