Tumor Size Predicts Synchronous Metastatic Renal Cell Carcinoma: Implications for Surveillance of Small Renal Masses

Abstract

Purpose: Active surveillance of small incidental renal masses is associated with slow radiographic growth and a low risk of metastatic progression. Radiographic tumor size, in the absence of histological data, is the only prognostic indicator available when considering active surveillance. To better define the relationship between tumor size and the metastatic potential of small renal masses, we investigated whether radiographic tumor size predicts for the presence of synchronous metastases in renal cell carcinoma. Materials and Methods: We reviewed our institutional tumor registry to identify sporadic pathologically verified renal cell carcinoma treated during an 8-year period. We analyzed data regarding primary tumor size and the presence of biopsy proven synchronous metastatic disease at presentation. All N+M0 and nonpathologically confirmed M+ disease was excluded from analysis. Results: We compared 110 cases of renal cell carcinoma with biopsy proven synchronous metastatic disease at presentation to 250 controls with clinically localized renal cell carcinoma. Tumors associated with synchronous metastasis were significantly larger than localized lesions (median 8.0 cm [range 2.2 to 20.0] vs 4.5 cm [range 0.3 to 17.5], p <0.0001). The probability of synchronous metastasis increased with increasing primary tumor size (p <0.0001). There were no patients with tumors 2 cm or smaller who presented with biopsy confirmed metastatic disease and less than 5% (5 of 110) of all synchronous metastasis occurred in tumors 3.0 cm or smaller. Logistic regression models determined that the odds of synchronous metastasis increased by 22% for each 1 cm increase in tumor size. Conclusions: Radiographic tumor size is a significant clinical predictor of the presence of biopsy proven synchronous metastatic renal cell carcinoma. In our series the odds of presenting with synchronous, biopsy proven metastatic disease increased by 22% with each 1 cm increase in tumor size. A 100% odds increase, or doubling of the risk of metastasis, occurs with a 3.5 cm increase in primary tumor size. These data have important implications for extent of disease evaluations in patients with large tumors and for the active surveillance of small enhancing renal masses.