Expression of stem cell phenotype (CD34) and multidrug resistance (MDR) on blast cells of 49 untreated patients with primary myelodysplastic syndromes (MDS) was studied by means of the alkaline phosphatase antialkaline phosphatase technique (APAAP). In 29 patients (59%) CD34 and in 19 patients (39%) MDR positivity was found. Both immunocytological markers showed a strong positive correlation (p<0.0005) and MDR expression was only detectable in CD34 positive cases. When comparing CD34 and MDR expression with well established prognostic parameters, medullary bone marrow (BM) blast percentage was found to be the sole variable which correlated with expression of both cell surface markers. CD34 and MDR negative patients had a better prognosis although only the difference between CD34 positive and CD34 negative cases reached statistical significance. Regarding the prognostic value of immunocytological results and other clinical and hematological parameters medullary blast cell infiltration remained the strongest predictive variable for survival and AML transformation. In 6 patients sequential immunocytological analysis during progression of disease were performed. In contrast to stable CD34 expression a marked increase in MDR expression after AML development could be noted in 2 cases.

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