Is the expression of multidrug resistance gene product a prognostic indicator for the clinical outcome of patients with renal cancer?

OBJECTIVE: To determine the significance of the expression of the multidrug resistance gene product (MDR-1) for the aggressiveness of renal cell carcinoma (RCC). PATIENTS AND METHODS: The study comprised 31 patients with clinically locally confined RCC treated with radical nephrectomy (mean age 64.1 years, range 41-78; mean follow-up 5.4 years, range 4.3-7.3). Their survival time and disease-free period were evaluated retrospectively. The expression of the MDR-1 gene product was determined immunohistochemically using the JSB-1 antibody in formalin-fixed paraffin-embedded tumour samples from these patients. The significance of this variable and tumour stage and malignancy grade was assessed for predicting the survival and disease-free period using Kaplan-Meier plots (log-rank test or Tarone's test) and the Cox multiple hazard regression analysis.
RESULTS: In a univariate analysis, tumour stage (P < 0.002), malignancy grade (P < 0.007) and MDR-1 (P < 0.03) were significant prognostic variables for both survival and disease-free period. Lower MDR-1 expression was correlated with poorer prognosis. On multivariate analysis, MDR-1 and tumour stage were significant factors for predicting the disease-free period, whereas tumour stage and malignancy grade were the most relevant factors for survival time. Calculating prognostic indices based on the results of the Cox analysis, MDR-1 could replace malignancy grade, resulting in a better prediction of survival and disease-free period (P < 0.001 vs 0.0031, P < 0.001 vs 0.021, respectively).
CONCLUSION: MDR-1, an established predictor for chemo-resistance, may also be a potent prognostic factor for outcome in patients with locally confined RCC. Moreover, MDR-1 expression seems to correlate with the differentiation of the RCC and thus its value as an objective measure of the degree of differentiation should be further explored.