Expression of myeloid antigens by blast cells in acute lymphoblastic leukemia of adults. The Southwest Oncology Group experience.

A subset of adult acute lymphoblastic leukemia (ALL) patients have blast cells which co-express myeloid-associated antigens (MY+ ALL). We have analyzed 113 adult ALL cases for expression of MY-associated antigens (MAA). ALL was diagnosed by standard morphology, cytochemistry, and immunophenotype in central review. MY+ ALL was diagnosed when > or = 20% of lymphoblasts co-expressed CD13 and/or CD33. Overall incidence of MY+ was 31/113 (27%). MAA expression was not significantly correlated with WBC, blast count, hemoglobin, or hematocrit. MY+ cases were more likely to express B-associated antigens, especially CALLA, and to be FAB L2, Ph+, or to have the BCR-ABL translocation by PCR, but these differences were not statistically significant. All patients were induced with a L10M regimen, and 67 (59%) achieved CR: 43/66 (65%) of B MY neg; 14/29 (48%) of B MY+; 10/16 (63%) T MY neg; and 0/2 T MY+. In age-adjusted analyses CR rate did not differ significantly between MY+ and MY neg patients or between B- and T-cell patients. Of the 113 patients, 84 have died and the remaining 29 patients have been followed for a median of 49 months. In proportional hazards regression analyses adjusting for age and WBC, heterogeneity of survival among the four groups was statistically significant (p = 0.021), largely due to MY status. The mortality rate was 85% greater for MY+ patients compared to MY neg patients (two-tailed p = 0.013). By contrast, survival did not vary significantly between B- and T-cell patients. The data indicate that MAA expression is useful for predicting overall survival of adult patients with ALL treated in a L10M protocol. As a predictive factor MAA expression is comparable to the WBC and superior to the more standard stratification by B- or T-cell markers for this group of patients.