Tumor Size Does Not Predict Risk of Metastatic Disease or Prognosis of Small Renal Cell Carcinomas

Purpose: We characterized the clinicopathological features and the prognosis of small solid renal tumors defined as tumors 4 cm or smaller.

Materials And Methods: We identified 1,208 patients who were treated with nephrectomy at 5 international academic centers for small solid renal tumors. Clinicopathological parameters and outcome data were collected for each patient and analyzed.

Results: Of the tumors 88% were renal cell carcinoma and 12% were benign. Of those with renal cell carcinoma 995 (93%) were localized (N0M0) and 72 (7%) presented with metastatic disease. Tumor size did not predict synchronous metastatic disease. The incidence of metastatic disease in the tumor size ranges 0.1 to 1.0, 1.1 to 2.0, 2.1 to 3.0 and 3.1 to 4.0 cm was 7%, 6%, 5% and 8%, respectively (p = 0.322). Survival rates were excellent. The majority of patients who died of renal cell carcinoma (54%) presented with synchronous metastatic disease, but 3% of patients with localized disease also died of renal cell carcinoma. In patients with localized disease there was a 7% chance of recurrence post nephrectomy at 5 years. Progression-free survival (28 months) was better than for patients with metastatic disease having a primary tumor greater than 4 cm (8 months). Tumor size was not retained as an independent prognostic factor of survival in multivariate analyses. The University of California Integrated Staging System and the Karakiewicz nomogram were the best predictors of cancer specific survival for all renal cell carcinoma stages (c-index 0.87).

Conclusions: More than 85% of small solid renal tumors are renal cell carcinoma. The majority of localized small renal tumors can be cured with existing surgical approaches. However, there is a small but not insignificant risk of synchronous and metachronous metastatic disease and cancer associated death. Patients considering experimental therapies such as ablation and surveillance should be aware of this. Tumor size alone is not sufficient to distinguish renal cell carcinoma with benign behavior from aggressive small renal cell carcinoma. Survival of patients with small metastatic renal cell carcinoma is better then expected. The biology of these unique tumors should be further studied.