Detection of cells with multidrug-resistant phenotype in myeloproliferative disorders before therapy.

The expression of the multidrug resistance (mdr) phenotype is connected with the overexpression of the P-glycoprotein. By applying the immunocytochemical assay, we have demonstrated that in myeloproliferative diseases (AML, ALL, MDS, CGL) in single cases in smear preparations from the peripheral blood as well as from the bone marrow P-glycoprotein-positive cells, respectively, cells with mdr-positive phenotype can be detected in the material obtained from patients before therapy and without clinically and anamnestically known exposure to cytotoxic or immunosuppressive drugs. In the control group of probands without hematologic disorders and also without clinically or anamnestically confirmed contact with cytotoxic or immunosuppressive drugs, we have found P-glycoprotein-positive subpopulations of cells with positive mdr phenotype in a few cases as well. The uniqueness of our results lies in the fact that this finding demonstrates the presence of subpopulations of mdr-positive cells in leukemias and myelodysplastic syndromes before therapy, and furthermore makes evident that a positive mdr phenotype is not necessarily associated with a malignant phenotype or a malignant cell transformation.