Background: The impact of mononuclear cell infiltration on renal cell carcinoma (RCC) biology has been controversial, previously reported to be associated with either a favorable or unfavorable prognosis. The objective of the current study was to evaluate associations between mononuclear cell infiltration in routinely prepared paraffin-embedded specimens with survival in patients with clear-cell RCC.

Methods: A total of 306 patients were identified treated with nephrectomy for clear-cell RCC between 1990 and 1994. A single urologic pathologist, blinded to patient outcome, reviewed the specimens and quantified the extent of mononuclear cell infiltration as absent, focal, moderate, or marked. Cancer-specific survival was estimated using the Kaplan-Meier method. Associations of mononuclear cell infiltration with death from RCC were assessed using Cox proportional hazards regression models.

Results: At last follow-up, 173 of the 306 patients studied had died, including 96 patients who died from RCC. Mononuclear cell infiltration was absent in 165 (54%), focal in 70 (23%), moderate in 53 (17%), and marked in 18 (6%). Univariately, patients with specimens that had mononuclear cell infiltration were over 2 times more likely to die from RCC compared with patients whose specimens exhibited no mononuclear cell infiltration (risk ratio, 2.63; P < .001). After adjusting for the Mayo Clinic SSIGN (stage, size, grade, and necrosis) score, patients with specimens that had mononuclear cell infiltration exhibited a significantly increased likelihood of dying from RCC compared with patients whose specimens had no mononuclear cell infiltration (risk ratio, 1.61; P = .028).

Conclusions: Mononuclear cell infiltration is associated with death from RCC even after multivariate adjustment. Routine documentation of mononuclear cell infiltration is recommended during the pathologic assessment of RCC.