CELL-SURFACE EXPRESSION OF THE MULTIDRUG-RESISTANCE P-GLYCOPROTEIN (P-170) AS DETECTED BY MONOCLONAL-ANTIBODY MRK-16 IN PEDIATRIC ACUTE MYELOID-LEUKEMIA FAILS TO DEFINE A POOR PROGNOSTIC GROUP - A REPORT FROM THE CHILDRENS CANCER GROUP

Expression of the multidrug resistance (MDR-1) gene product, P-glycopr otein (P-170), and the stem cell antigen, CD34, at diagnosis were dete rmined using monoclonal antibodies (MoAbs) MRK-16 and 12.8, respective ly, in 130 pediatric acute myeloid leukemia (AML) patients entered ont o Childrens Cancer Group (CCG) study CCG-2891. Fluorescein isothiocyan ate (FITC) as a second step reagent was employed for the measurement o f P-170 expression since it is commonly used in clinical laboratories. Nine of 30 (30%) infant (<1 year of age) de novo specimens expressed P-170 at levels greater than or equal to 20% of control cells. In cont rast, eight of 100 (8%) AML samples from older children (greater than or equal to 1 year of age) expressed the multidrug resistance surface protein at diagnosis. With the exception of one infant, all de novo sa mples that expressed P-170 also expressed CD34. Pediatric patients of any age with positive P-170 expression using MoAb MRK-16 with a FITC-c onjugated second step reagent fared no worse than remaining patients t reated on the same treatment with regard to induction failure, inciden ce of relapse, event-free survival, or overall survival. Further inves tigation is necessary to determine whether P-170 assay systems with gr eater sensitivity will distinguish pediatric AML patients with poor pr ognosis.