pT1 clear cell renal cell carcinoma: A study of the association between MIB-1 proliferative activity and pathologic features and cancer specific survival

BACKGROUND. The majority of patients with pT1 clear cell renal cell carcinoma (RCC) are cured with nephrectomy. However, a few patients will die of RCC. In several studies, MIB-1 proliferative activity was identified as an independent predictor of survival in patients with RCC. The objective of the current study was to examine MIB-1 proliferative activity in a large series of patients with pT1 clear cell RCC who were treated uniformly with radical nephrectomy, and to examine the association between proliferative activity and cancer specific survival in a multivariate model incorporating tumor size, nuclear grade, and tumor necrosis. METHODS. Patients with solitary pT1 clear cell RCC who underwent radical nephrectomy between 1970-1997 were eligible for the current study. For each of the 40 patients who died of RCC, a stratified random sample of at least 3 year-matched patients who still were alive or had died of other causes at the time of last follow-up was selected. Patient age at nephrectomy, patient gender, tumor size, nuclear grade, and tumor necrosis were evaluated, and the MIB-1 proliferative activity was assessed using digital image analysis. Univariate and multivariate Cox proportional hazards models were fit to assess the features associated with cancer specific survival. The associations between MIB-1 proliferative activity and pathologic features were assessed using the Wilcoxon rank sum test. RESULTS. The mean MIB-1 value for those patients who died of clear cell RCC was 6.5% compared with 3.6% for those patients who died of other causes or were still alive at the time of last follow-up. Patients whose tumor had an MIB-1 proliferative activity ≥ 5.0% were more than twice as likely to die of RCC than patients whose tumors had a MIB-1 activity < 5% (P = 0.02). However, after adjusting for tumor size, nuclear grade, and necrosis, MIB-1 proliferative activity was not found to be associated significantly with cancer specific survival. There was a significant association between MIB-1 proliferative activity and tumor size, nuclear grade, and necrosis. CONCLUSIONS. After adjusting for tumor size, nuclear grade, and necrosis, MIB-1 proliferative activity was not found to be an independent predictor of outcome in patients with pT1 clear cell RCC who were treated with radical nephrectomy. There was a significant association between MIB-1 and other well established pathologic prognostic features of pT1 clear cell RCC.