Renal cell carcinoma (RCC)is the most common type of kidney cancer. RCC begins small and grows larger over time, like many other cancers. Based on limited observations, renal cancers appear to grow approximately 1 cm (1/2 inch) in diameter per year. RCC usually grows as a single mass. Sometimes, a kidney may contain more than one tumor or tumors may be found in both kidneys at the same time.