Detection of the multidrug resistance marker P-glycoprotein by immunohistochemistry in malignant lung tumours.

BACKGROUND The multidrug resistance marker P-glycoprotein (P-gp) was studied immunohistochemically in 78 primary malignant lung tumours. 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 chemotherapy. Certain normal tissues express P-gp and tumours derived from these tissues are often insensitive to cytotoxic agents, showing raised P-gp levels innately or following chemotherapy or radiotherapy. METHODS Samples from 78 patients undergoing surgery for primary malignant lung tumours were snap frozen and stained immunohistochemically using the monoclonal antibody C219 which reacts with a P-gp epitope. None of the study group had received chemotherapy or radiotherapy before surgery was performed. RESULTS Twenty seven of the 78 lung tumours (34.6%) showed immunohistochemically detectable levels of P-gp which varied with tumour type; 17 of 54 squamous cell carcinomas (31.5%), seven of 15 adenocarcinomas (46.7%), and neither of two small cell carcinomas 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 tumours before exposure to radiotherapy or drugs associated with multidrug resistance. It may have a role in tumour resistance to cytotoxic drugs, but further clinical studies will be required to evaluate any correlation between P-gp levels and response to treatment.