MULTIDRUG-RESISTANCE GENE (MDR-1) EXPRESSION IN NEURO-AXIAL TUMORS OFCHILDREN AND YOUNG-ADULTS

Drug resistance in many cancers outside the CNS has been associated wi th over-expression of the multidrug resistance gene (MDR1), which code s for the transmembrane efflux pump P-glycoprotein (Pgp). To determine whether rumours of the neuroaxis over-express MDR1 and to identify th e site of Pgp expression we examined 50 tumour specimens from 46 child ren and young adults using immunocytochemistry. Pgp was not expressed by any neoplastic cells, but was detected in the endothelium of tumour blood vessels in 35 of the 50 samples (70%). 11/35 (31%) were Pgp pos itive in the majority of vessels, 11/35 (31%) in a proportion, but <50 % of vessels, and 13/35 (37%) in one or two vessels. Pgp was also dete cted in surrounding normal brain capillaries. MDR1 may play a role in the chemoresistance of neuro-axial tumours either by its expression in the normal blood-brain barrier or by forming a blood-tumour barrier. The proportion of vessels expressing Pgp may determine the degree of r esistance.