Does P-glycoprotein-170 expression predict for chemoresistance in transitional cell carcinoma of the bladder?

Introduction: The glycoprotein P-170, causing drug efflux from the cells, may represent at least one cause of resistance to most drugs used in intravesical chemotherapy of superficial bladder cancer.
Materials and Methods: GP-170 was retrospectively assessed in 60 patients affected by superficial transitional cell tumours of the bladder. It was assessed by immunohistochemistry in a semiquantitative way by the intensity of staining and by the percentage of positive cells. Correlation of GP-170 expression with G-grade, T-category, multiplicity, recurrence rate and treatment was investigated. In 44 patients recurrence was analysed in relation to GP-170 basal expression and to its variations. The monoclonal antibody JSB1 (DBA) at 1:20 dilution was employed for the GP-170 assay.
Results: GP-170 expression increases with grade but was lower in multiple tumours. No difference between Ta and T1 categories was detected. GP-170 immunohistochemistry from different portions of the same tumour showed a very marked variability in 35.7% of patients. Seven patients (11.6%) were totally negative for GP-170. No statistically significant correlation was found between recurrence, progression and GP-170 basal expression. Similarly no correlation emerged between grade and stage variations at recurrence and modifications in GP-170 expression. One third of the tumours recurring after chemotherapy were negative for GP-170 in spite of an increase in recurrence rate and other risk factors.
Conclusion: At the present stage of our experience, we have been unable to show that GP-170 is a useful marker for monitoring chemoresistance to intravesical chemotherapy in superficial bladder cancer. Furthermore, GP-170 determination has shown several technical difficulties.