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Here's more bad news for smokers: Puffing cigarettes increases the likelihood of developing the deadliest form of kidney cancer.

The finding from Duke University Medical Center researchers offers new insights into the direct role smoking plays in advanced renal cancer, but it also comes with a motivational message.

"If you stop smoking, the risk stops," said Matvey Tsivian, MD, a Duke urologic oncology fellow and lead author of the study published online April 18, 2011, in the Journal of Clinical Oncology. "And the longer you stop smoking, the better it is."

Tsivian and colleagues reviewed the smoking histories of 845 Duke patients who had undergone surgery for kidney cancer from 2000 to 2009. Of those, 164 were current smokers, 246 had quit, and the remaining 435 never took up the habit.

Current and former smokers were more likely than non-smokers to have advanced renal cancer, defined as a tumor that involves the lymph nodes or has otherwise spread.

Advanced malignancies are much more lethal than early stage renal cancers. Only 8 percent of patients with the most severe form of renal cancer survive five years, according to the American Cancer Society, while five-year survival rates top 70 percent among early stages of kidney cancer.

The Duke researchers found that advanced disease was diagnosed in only 20.2 percent of the nonsmokers in the study group, compared to 28.7 percent of the current smokers, and 29.3 percent of the former smokers -- some of whom had been addicted for decades before they quit.

"The actual mechanisms of how smoking may affect cancer growth are unknown," Tsivian said. He added that tobacco smoke has long been associated with genetic mutations, inflammation, and cellular damage -- all of which fuel cancer growth.

But by quitting, smokers lower their chances of developing severe kidney cancer. The Duke researchers found that every decade spent smoke-free resulted in a 9 percent reduction in the odds of being diagnosed with advanced disease.

"The more durable the cessation is, the more it lowers risk," Tsivian said, although quitting doesn't completely negate harm.

Tsivian said those who quit for at least 20 years have a 22 percent risk of developing advanced kidney cancer, compared to a non-smoker's 20 percent risk.

"There is a clear relationship between heavier smoking and the development of advanced renal cell carcinoma," said Dr. Thomas J. Polascik, director of Urologic Oncology at the Duke Cancer Institute and senior author of the study.

"The good news is that smoking cessation can revert those risk factors over time. This should provide the public with another reason to quit smoking. It is not too late."

In addition to Tsivian and Polascik, study authors included Daniel M. Moreira, MD, Jorge R. Caso, MD, and Vladimir Mouraviev, MD. The research was supported by Duke.