Initial P-glycoprotein expression in childhood acute lymphoblastic leukemia: no evidence of prognostic impact in follow-up.
Treatment results in childhood acute lymphoblastic leukemia (ALL) have improved remarkably during the past 20 years, but still 25% of children cannot be permanently cured. Drug resistance is a major cause of poor outcome. One of the most investigated resistance mechanisms is the P-glycoprotein (P-gp)-mediated multiple-drug resistance (MDR). The authors prospectively analyzed P-gp using flow cytometry with monoclonal antibody JSB1 in a population-based series of 103 children with ALL treated according to intensive Nordic ALL protocols. Increased P-gp expression was detected in 55 patients (53%). With a cutoff value of 1% P-gp-positive blasts in bone marrow, no difference was found in event-free survival (EFS) or overall survival between children with low vs. increased P-gp expression. The 4-year EFS in the whole series was 77%. Patients with T-ALL had higher P-gp levels than the others, 3.6% vs. 1.0% (p = .002). P-gp expression did not correlate with the white blood cell count, age, sex, or cytogenetics. The authors conclude that the level of P-gp expression cannot be used as a tool for treatment stratification in childhood ALL.