Clinical importance of myeloid antigen expression in adult acute lymphoblastic leukemia.

To determine the clinical importance of immunophenotypes in adult acute lymphoblastic leukemia (ALL), we prospectively studied 76 patients with this condition. Before treatment, lymphoblasts were tested for reactivity with monoclonal antibodies to B-cell, T-cell, and myeloid (My) antigens. Unexpectedly, myeloid antigens (MCS-2 or MY9) were identified in 25 patients (33 percent), usually in conjunction with B-cell or T-cell antigens. Among My+ patients, 15 (60 percent) expressed B-cell antigens (B+T-My+); all 6 tested had rearranged immunoglobulin genes. Five patients (20 percent) expressed T-cell antigens (B-T+My+), and one My+ patient expressed both B-cell and T-cell antigens. Only myeloid antigens (B-T-My+) were expressed in four patients (16 percent); three who were tested had germ-line immunoglobulin and T-cell-receptor gene configurations. Although no significant differences in presenting clinical features were found, My+ patients had fewer complete remissions than My- patients (35 vs. 76 percent, P less than 0.01). No differences in response or survival were observed between My+ and My- patients expressing T-cell antigens. However, among those expressing B-cell antigens, My+ patients had fewer complete remissions (29 vs. 71 percent, P = 0.02) and shorter survival (P = 0.03; median, 8.1 vs. greater than 26 months). These findings indicate that expression of myeloid antigen identifies a high-risk group of patients with adult ALL for whom alternative forms of treatment should be investigated.