DETECTION OF THE MULTIDRUG-RESISTANCE MARKER P-GLYCOPROTEIN BY IMMUNOHISTOCHEMISTRY IN MALIGNANT LUNG-TUMORS

Background - The multidrug resistance marker P-glycoprotein (P-gp) was studied immunohistochemically in 78 primary malignant lung rumours. P -gp is a 170 kD transmembrane ATP dependent drug efflux pump which has been shown to be important in the resistance of some tumours to chemo therapy. Certain normal tissues express P-gp and tumours derived from these tissues are often insensitive to cytotoxic agents, showing raise d P-gp levels innately or following chemotherapy or radiotherapy. Meth ods - Samples from 78 patients undergoing surgery for primary malignan t lung tumours were snap frozen and stained immunohistochemically usin g the monoclonal antibody C219 which reacts with a P-gp epitope. None of the study group had received chemotherapy or radiotherapy before su rgery was performed. Results - Twenty seven of the 78 lung tumours (34 .6%) showed immunohistochemically detectable levels of P-gp which vari ed with tumour type; 17 of 54 squamous cell carcinomas (31.5%), seven of 15 adenocarcinomas (46.7%), and neither of two small cell carcinoma s showing positive staining. In six of seven cases normal respiratory epithelium present showed the presence of P-gp. Conclusions - P-gp is immunohistochemically detectable in frozen tissue from a proportion of malignant lung rumours before exposure to radiotherapy or drugs assoc iated with multidrug resistance. It may have a role in tumour resistan ce to cytotoxic drugs, but further clinical studies will be required t o evaluate any correlation between P-gp levels and response to treatme nt.