Metastatic Potential in Renal Cell Carcinomas ≤7 cm: Swedish Kidney Cancer Quality Register Data

BackgroundRenal cell carcinoma (RCC) represents 2–3% of all malignancies and accounts for approximately 90% of all kidney malignancies. An increasing proportion of RCCs are discovered incidentally, and the average tumor diameter at diagnosis has decreased over the last few decades. Small RCCs have often been regarded by many as relatively harmless.ObjectiveThe objective was to evaluate the incidence of local T-category distribution and lymph node and distant metastases in relation to tumor size in RCCs ≤7 cm in a nationally based patient population.Design, setting, and participantsData were extracted from the National Swedish Kidney Cancer Register containing 3489 RCCs diagnosed between 2005 and 2008. This is a population-based registry including 99% of all RCCs diagnosed nationwide. The study included 2033 patients having a tumor ≤7 cm in diameter.MeasurementsThe size of the tumors was compared with sex, age, cause of diagnosis, Fuhrman grade, RCC type, and TNM category.Results and limitationsMost RCCs were discovered incidentally and incidence correlated inversely to tumor size. There were 887 (43%) patients with category T1a tumors, 836 (40%) with category T1b, 174 (8%) with T3a, 131 (6%) with T3b/c, and 12 (1%) patients had invasion of adjacent organs (T4). A total of 309 (15%) patients had lymph node and/or distant metastases. Of the 177 1- to 2-cm RCCs, category T3 tumors were identified in three patients and lymph node and/or distant metastases were identified in 8 (5%). Only for tumors ≤1 cm was there neither advanced stage nor metastasis. The occurrence of locally advanced growth, lymph node and distant metastases, and high tumor grade correlated to tumor size. Patients with Fuhrman grade III or IV had a four-fold greater risk of metastases than grades I or II.ConclusionsLymph node and distant metastases occur even in small RCCs. Risk of metastases increases with tumor size. The data clearly show that small RCCs also have a malignant potential and should be properly evaluated and adequately treated.