The number of cases of kidney cancer has been rising over the last two decades, and new research from the University of Michigan Comprehensive Cancer Center shows that this increase is driven largely by the detection of small, presumably curable, kidney masses. But even though the rising incidence has been paralleled by greater use of surgery for kidney cancer, this trend has not led to fewer people dying.
"With increased early detection and treatment of small tumors, we would expect to see a decrease in mortality associated with kidney cancer," says senior author Brent K. Hollenbeck, M.D., assistant professor of urology at the U-M Medical School. "Surprisingly, that's not what we found. Our research shows that an increase in detection and treatment is not leading to a reduction in the kidney cancer mortality rate."
The study - published in the Sept. 20 issue of the Journal of the National Cancer Institute - includes data from nine of the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) registries. In all, the researchers examined data from 34,503 patients with kidney cancer.
Over the study period (1983 to 2002), researchers observed a rise in the occurrence of kidney cancer (also known as renal cell carcinoma) for tumors of all sizes. But the greatest increases in kidney cancer incidence were among tumors 4 centimeters or smaller. Tumors of this size, often found in patients without any clinical signs or symptoms, are being detected more and more with the widespread use of abdominal imaging studies, such as MRIs and CAT scans. These small kidney tumors are considered curable by surgery, which has led to a rise in surgery for kidney cancer.
Even as early detection and surgical treatment increased, however, mortality rates caused by kidney cancer during the time period rose dramatically, from 1.2 to 3.2 deaths per 100,000 people in the United States.
These seemingly contradictory findings can be explained, in part, through the rising incidence of larger, more lethal tumors, says lead author John M. Hollingsworth, M.D., fifth-year surgery resident with the Department of Urology at the U-M Medical School. "While more and more small, detectable kidney tumors are being treated, the absolute number of patients with larger, lethal masses has not decreased. And it is these larger, lethal masses that seem to mainly affect mortality," Hollingsworth says.
The researchers say the data also suggest something else: A proportion of these smaller, incidentally found kidney tumors may not merit surgical removal.
"We're not saying that surgery for patients with small renal masses is inappropriate," Hollingsworth says. "Our findings, however, show that their increased treatment has not diminished kidney cancer mortality. This calls to question the effectiveness of our current treatment strategy. Perhaps there are some patients with small kidney tumors for whom surgery is not the best option."
Kidney cancer is the third most common malignancy of the genitourinary system (the reproductive system and urinary system). The American Cancer Society estimates there will be about 38,890 new cases of kidney cancer (24,650 in men and 14,240 in women) in the United States this year, and about 12,840 people (8,130 men and 4,710 women) will die from the disease.
This study included data from 34,503 kidney cancer patients, including age at diagnosis, race, gender and information about the tumor. During the years 1983-2002, researchers found, the overall incidence of kidney cancer rose from 7.1 to 10.8 cases per 100,000 people in the United States, an increase of 52 percent. The largest increase was among people with tumors 2 to 4 centimeters in size (the second-smallest category of tumors in the study), an increase of 1.0 to 3.3 cases per 100,000 people in the United States.
Mortality rates also increased, most notably among people with the largest group of tumors (greater than 7 centimeters). Deaths caused by cancer in this group rose from 0.3 to 1.4 per 100,000 people in the United States.
"What this shows us is that, despite more frequent surgeries for smaller kidney cancers, mortality among patients with kidney cancer has continued to increase," Hollingsworth says. "So even while detection and treatment are increasing and more tumors have become detectable, this study suggests a disconnect because we are not decreasing mortality rates."
In addition to Hollingsworth and Hollenbeck, researchers on the study were David C. Miller, M.D., clinical lecturer in the Department of Urology; and Stephanie Daignault, M.S., a biostatistician with the U-M Comprehensive Cancer Center.
The research was supported by a training grant from the National Institutes of Health, and funding from the Johan and Suzanne Munn Endowed Research Fund of the University of Michigan Comprehensive Cancer Center.