Various mechanisms are involved in drug resistance of tumor cells. Among them one such mechanism is the overexpression of the multidrug resistance(mdr1) gene product P-glycoprotein(Pgp) that functions as an energy - dependent drug efflux pump.

The expression of P-glycoprotein by immunohistochemistry was examined in 20 cases of laryngeal squamous cell carcinoma and vocal nodules as a control pump using a newly developed monoclonal antibody(MDR/JSB-1) which is specipic to human mdr1 gene product and recognizes an external epitope of the protein. Mdr1 gene product expression was compared with clinical response to chemotherapy in six patients who received mdr1 dependent drugs.

The results are summerized as follows.

1) Among 20 laryngeal cancer tissues, P-glycoprotein was detected in 8 patients and none of 20 vocal nodules showed expression of P-glycoprotein.

2) There is a correlation in between positive P-glycoprotein staining and tumor differentiation.

3) No correlation in between positive P-glycoprotein standing and tumor stage of tumor site is observed.

4) 2 patients with negative clinical response to chemotherapy among 6 patients who received inductive chemotherapy with cisplatin, vincristine and p pepleomycin revealed positive P-glycoprotein staining.

Therefore, analyzing the expression of P-glycoprotein may play a role when planning chemotherapeutic regimens for patients with head and neck cancer and may be an additional prognostic and diagnostic tools in these patients.