Tumor Size is a Determinant of the Rate of Stage T1 Renal Cell Cancer Synchronous Metastasis

Purpose: A recent multi-institutional analysis of 995 patients treated for renal cell cancer questioned the relationship between tumor size and the synchronous metastasis rate. We revisited the hypothesis that metastatic potential is unrelated to tumor size. Materials and Methods: We tested the relationship between tumor size and synchronous metastasis in 22,204 patients with T1a and T1b renal cell cancer diagnosed and/or treated with nephrectomy for clear cell, papillary or chromophobe histological subtypes in 1 of 9 Surveillance, Epidemiology and End Results registries between 1988 and 2004. Results: In the study population the synchronous metastasis rate was 9.6%, including 5.6% vs 14.2% for T1a vs T1b. Stratification by 1 cm tumor size intervals revealed that the rate increased with increasing tumor size, that is 4.8% at 1.0 cm or less, 4.2% at 1.1 to 2.0 cm, 4.9% at 2.1 to 3.0 cm, 7.1% at 3.1 to 4.0 cm, 12.1% at 4.1 to 5.0 cm, 13.3% at 5.1 to 6.0 cm and 18.4% 6.1 to 7.0 cm (chi-square trend p < 0.001). Cubic spline analysis showed that tumor size was virtually linearly related to the synchronous metastasis rate. Stratification by histological subtype in patients treated with nephrectomy revealed that clear cell renal cell cancer was most frequently associated with synchronous metastasis. Finally, tumor size was an independent predictor of synchronous metastasis in multivariate regression models adjusted for age, gender, histological subtype and year of diagnosis quartiles. Conclusions: Our study confirms that tumor size is an important determinant of the likelihood of synchronous metastasis in patients with T1a and T1b renal cell cancer. The synchronous metastasis rate directly increases with increasing tumor size. Even patients with small renal masses are at risk for synchronous metastasis and patients with clear cell renal cell cancer are at highest risk.