P-glycoprotein expression in the squamous cell carcinoma of the tongue base.

P-glycoprotein (PGP), which is a product of the multidrug resistance gene (MDR1), is an active transmembrane efflux pump responsible for detoxifying normal cells as well as rendering tumor cells resistant to chemotherapy. It has also been implicated to be expressed by more aggressive cancers. It has not been well described in squamous cell carcinoma of the head and neck. In this investigation, an attempt was made to characterize advanced squamous cell carcinoma of the base of tongue with respect to expression of PGP. Using immunohistochemical techniques two anti-PGP monoclonal antibodies (JSB1 and C494) were used to detect PGP in these lesions, and an attempt was made to correlate levels of PGP staining and various tumor parameters. Usefulness of PGP in predicting survival and time to recurrence was also examined for these advanced lesions. All 33 base of tongue lesions showed staining for PGP with these monoclonal antibodies. This was the first study examining utility of C494 in detecting PGP in squamous cell carcinoma at this site. Increased level of PGP expression was seen in better-differentiated tumors as well as in tumors with diploid DNA. A trend of higher PGP expression and decreased survival emerged. This may represent a true relationship, but inherent heterogeneity of PGP expression within cells cannot be excluded. Both antibodies examined appear to be useful in the investigations of PGP distribution in squamous cell carcinomas of the head and neck sites by immunohistochemical techniques. Prognostic value of the level of PGP expression remains to be seen.