Thirty-four children with newly diagnosed acute nonlymphoblastic leukemia were analysed for the expression of P-glycoprotein (P-170), glutathione S-transferase-pi, (GST-pi) topoisomerase II (Topo II) and the proliferation antigen Ki-67 by the streptavidin-biotin-peroxidase method. Overexpression of P-170 was present in 26 cases (76%) and GST-pi overexpression was seen in 11 patients (32%). Down regulation of Topo II was found in 16 patients (47%) and Ki-67 positive cells (>5%) were detectable in 9 patients (26%). The remission rate was not influenced by P-170 or GST-pi expression, whereas patients with down regulation of Topo II or low Ki-67 expression had lower remission rates. The data were not significant. The probability of continuous first remission (CR) was lower in patients with P-170 expression (p=0.09). A significantly lower probability of CR was also seen in patients with low proliferative activity (p=0.03, log-rank test). The expression of the resistance proteins and the proliferative activity were found to be independent of the clinical parameters age, sex, FAB-type, and initial white blood cell count.

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