Expression of P-glycoprotein in de novo acute myelogenous leukemia at initial diagnosis: results of molecular and functional assays, and correlation with treatment outcome.

We investigated the expression of P-glycoprotein (P-gp) in 52 adults with de novo acute myelogenous leukemia (AML) at the initial diagnosis. We tested 52 patients by flow cytometry using the MRK16 monoclonal antibody (MoAb). To investigate the phenotype for multidrug resistance, 41 of the patients were analyzed using rhodamine 123 (Rh123). We found that 14 (27%) of the 52 patients were positive for P-gp expression by MRK16 MoAb using a cutoff of 5% positive cells. There was a significant correlation between the results of the two analyses (p < 0.01). We suggest that flow cytometry using MRK16 MoAb is acceptable for use in detecting P-gp expression in clinical samples. Among the 52 patients, 43 (83%) obtained a complete remission (CR) and 45% of remitters were predicted to be alive and in a CR after 8 years. Although the rate of CR on the MRK16-positive patients was comparable to that of the MRK16-negative patients, the MRK16-positive patients were prone to relapse. We conclude that determination of P-gp expression of de novo AML at initial presentation did not significantly influence the outcome of treatment.