Obesity linked to clear-cell kidney cancer

NEW YORK (Reuters Health) - Although obesity is a well known risk factor for kidney cancer, the link seems to be specific to clear-cell renal cell carcinoma (RCC), a report in the January issue of BJU International shows.

Using a renal surgery database of 1640 patients, doctors at Memorial Sloan-Kettering Cancer Center in New York City found that for each one-point increment in body mass index (BMI), the adjusted odds of having clear-cell RCC rose 4% (p<0.001).

The median age in the cohort was 62 years, and the median BMI was 28 kg/m2. Ninety-one percent (1492 patients) had malignant tumors, and 63% (1033 patients) had clear-cell RCC.

Rates of obesity (i.e., BMI 30 kg/m2 or higher) were 38% overall, 31% in patients with benign pathology, and 42% in patients with clear-cell tumors.

Obese patients had 48% higher odds of having clear-cell RCC than patients with a BMI below 30 (p<0.001). Obesity was not associated with other histologic findings, such as benign pathology or papillary RCC.

"This is a very good study," said medical oncologist Dr. Toni Choueiri, director of the Kidney Cancer Center at Dana-Farber Cancer Institute and Brigham and Women's Hospital, who was not involved in the new research. "It's well designed and it brings something new to the table."

But, Dr. Choueiri added, while "it's something to be aware of...this is only the first step," because the study was retrospective and uncontrolled.

Kidney cancer has been on the rise in the U.S. over the past few decades, with incidence rates climbing by 2% to 5% annually since the 1970s. The lifetime risk is now about one in 75, according to the American Cancer Society. Clear-cell carcinoma is one of the most aggressive forms.

Improved diagnostic tools might account for part of the increase, but soaring obesity levels may play a role, too, researchers suggest.

If confirmed by other studies, the link between fat and clear-cell RCC -- the most common kidney cancer -- could have clinical repercussions. "I think there is potential that it can affect how patients are managed, especially for small cell masses," said urologic oncologist Dr. William Lowrance of Sloan-Kettering, who led the new study.

Currently, he added, some patients with small kidney tumors are just observed. If the new findings are confirmed, doctors may choose to manage obese individuals more aggressively.

So far, the mechanism tying obesity to kidney cancer is unknown, but both estrogen and insulin-like growth factor could be involved, according to Dr. Lowrance, who hopes his results will inspire more in-depth studies.

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