Forty years ago, about 30,000 Americans were diagnosed every year with kidney cancer. Today, that number is 60,000. Is it an epidemic? No, it’s the increasing use of CT scans for other problems.

“More and more kidney masses are discovered by chance,” notes Alice Semerjian, M.D., the Warburton-Jewett Urologic Oncology Fellow. “Most of these are localized and considered to be small renal masses, measuring less than 4 centimeters.” The standard management of kidney masses is surgical removal, but in recent years – in a shift led by Brady researchers – many people with small renal masses are choosing active surveillance instead.

Which tumors can safely be followed? In a study led by Semerjian, Brady investigators systematically reviewed the kidney cancer literature, identified six high-quality studies that described tumor pathology by size and combined these studies with data from the Johns Hopkins Renal Mass Database. “Lowrisk tumors were defined as benign or low-grade cancers confined to the kidney,” Semerjian explains, “tumors that are believed not to grow or metastasize during a patient’s lifetime.”

The study showed that the vast majority – greater than 90 percent of tumors 2cm or smaller, and 80 percent of tumors smaller than 4 cm – of small renal masses are low-risk. Using U.S population-based data, Semerjian and colleagues estimated between 17,935 and 24,821 patients each year undergo kidney surgery for a lowrisk tumor – surgery that they probably don’t need. These findings were presented at the American Urological Association’s Annual Meeting in Boston.

“We know that most small renal masses are not dangerous,” says the study’s senior author, Phillip Pierorazio, M.D. “This study certainly puts into perspective the number of patients undergoing potentially unnecessary surgery and highlights the role of active surveillance in the initial management of many patients with small renal masses.”

But not all small tumors are safe, Pierorazio adds: “Some small renal masses can be dangerous, and this study highlights the need for better diagnostics – including blood, urine and imaging tests – to inform patients and providers about the risks associated with their mass.