Determination of the cutoff value of the proportion of cystic change for prognostic stratification of clear cell renal cell carcinoma

Purpose: Cystic renal cell carcinoma has more favorable biology than noncystic renal cell carcinoma. Recently cystic change detected grossly or by low power microscopy was found to be a good prognostic factor for clear cell renal cell carcinoma. We assessed the optimal cutoff value of the proportion of cystic change with prognostic significance for clear cell renal cell carcinoma. Materials and Methods: We identified 223 patients with clear cell renal cell carcinoma who underwent partial or radical nephrectomy between 2001 and 2003. The cystic proportion of the tumor cut surface was calculated objectively and its prognostic significance was evaluated. Results: The ROC curve showed that a cystic percent of between 6% and 10% was appropriate to detect patients with renal cell carcinoma at low risk for cancer mortality and progression. A cutoff of 6% was adopted as a break point of cystic change for patient stratification. We analyzed the records of 87 patients (39.0%) with tumors with a cystic proportion of greater than 5%, that is 6% or greater. They had significantly lower stage and lower Fuhrman nuclear grade than patients with tumors with a cystic change of 5% or less (each p <0.0001). On multivariate analysis a cystic proportion of more than 5% was a good prognostic indicator of cancer specific and progression-free survival (HR 0.221, p = 0.044 and HR 0.214, p = 0.004, respectively). Conclusions: In patients with clear cell renal cell carcinoma a cystic change comprising more than 5% of the tumor is a good independent predictor of survival.