Researchers have found that kidney cancer is not only more common among heavy smokers, it also appears to be more aggressive.

According to a study out Monday, more than one in four smokers undergoing kidney cancer surgery had advanced stages of the disease, compared to only one in five patients who didn’t light up.

Researchers say about 70 percent of people with early-stage tumors survive at least five years, whereas that number plummets to just eight percent after the cancer has begun spreading.

About one in 70 Americans, most of them elderly, develop kidney cancer, according to the American Cancer Society.

But the findings aren’t all bad news. Indeed, former smokers who’d kicked the habit had a smaller chance of turning up with advanced cancer.

While the study wasn’t designed to prove that quitting can slow tumor growth, Dr. Thomas J. Polascik, who led the work, said he believes that to be the case.

“It can’t bring you down to the risk of a nonsmoker, but it can get you almost there,” Polascik, a surgeon at Duke University in Durham, North Carolina, told Reuters Health. His findings appear in the Journal of Clinical Oncology.

Polascik and his colleagues looked at data for 845 people who’d had surgery for kidney cancer at their hospital. A quarter of the patients had advanced disease, defined as cancer spreading beyond the kidney.

The odds of finding late-stage cancer were 60 percent higher in smokers - about a fifth of the patients - than non-smokers, even after taking age and other factors into account. And the more cigarettes they had smoked, the higher the odds.

Former smokers also had higher odds of advanced disease. But the odds fell by nine percent for every decade they had been smoke-free.

The researchers say that means smoking might not only up the chances the a tumor will form in the first place, but might also fuel cancer growth, perhaps by suppressing the immune system.

However, Alexander S. Parker, a kidney cancer expert at the Mayo Clinic in Jacksonville, Florida, said it’s also possible that smokers are less likely to seek medical care than non-smokers.

“If this is true, then it would not be the case that the biology of these tumors is different,” he told Reuters Health in an email. “Rather, just that the individuals themselves have less contact with the health care system and are less likely to be diagnosed when their cancers are at an early, treatable stage.”

Still, Parker, who was not involved in the new work, said the findings lined up with earlier data showing that smokers have twice the risk of developing kidney cancer, in addition to other health problems.

“In the end,” he said, “we need to be clear that smoking accounts for hundreds of thousands of deaths every year in the U.S. and therefore, the overall effort should still be focused on getting people to quit smoking and to keep young people from starting in the first place.”

SOURCE: Journal of Clinical Oncology, online April 18, 2011.