(Reuters Health) - Prostate cancer patients who smoke are more likely to have tumors return, spread to other parts of the body, and become fatal than nonsmokers, a new study suggests.

Researchers examined data from previous studies with a total of 22,549 men with prostate cancer that hadn’t spread to other parts of the body. The cancers were treated with either surgery or radiation.

Overall, nearly one in five were current smokers. The rest were either former smokers or had never smoked.

The researchers tracked half the men for at least six years. During follow-up, compared to men who never smoked, current smokers were 40 percent more likely to have tumors return after treatment and more than twice as likely to have cancer spread beyond the prostate. Smokers were also 89 percent more likely to die from cancer.

“Prostate cancer diagnosis, even when it is not associated with tobacco smoking, is a teachable moment for patients to quit smoking,” said senior study author Dr. Shahrokh Shariat of the Medical University of Vienna in Austria.

“Former smoking was associated with higher risk of relapse, but not with spread or cancer-specific death, which underlines the importance of smoking cessation in improving disease outcome,” Shariat said by email. In fact, he added, men who had stopped smoking more than 10 years earlier “were not significantly different than patients who had never smoked.”

Not all men with localized prostate tumors get aggressive treatment with surgery or radiation. Often, men with these types of tumors will opt for more conservative alternatives, such as watchful waiting or hormone therapy to shrink tumors without surgery or radiation.

Smoking has long been linked to an increased risk of death from a range of malignancies including tumors of the lung, bronchus, trachea and larynx, stomach and kidney.

“We know that tobacco smoking produces more than 70 carcinogens,” Shariat said.

It’s not clear exactly how smoking might lead prostate cancer to develop or make it more aggressive or more fatal. One possibility is that smoking causes inflammation, which in turn encourages tumors to grow, or that nicotine leads malignancies to spread, Shariat said.

The smaller studies in the current analysis that looked at cancer-related deaths had a total of 7,924 participants. Overall, 654 men, or about 8 percent, died by the time researchers had followed half of them for about eight years.

The current study wasn’t a controlled experiment designed to prove whether or how smoking influences the odds of dying from prostate cancer. Researchers also based the analysis on smoking status when patients were in treatment, and it’s possible some patients might have stopped or started smoking after that.

Smokers also might be less compliant with treatment than nonsmokers, said Dr. Stephen Freedland, author of an accompanying editorial and director of the Center for Integrated Research on Cancer and Lifestyle at Cedars-Sinai Medical Center in Los Angeles.

But because the study looked at men undergoing aggressive treatment, it’s unlikely that noncompliance influenced patient outcomes, Freedland said by email.

“Cigarettes themselves have chemicals that can cause cancer,” Freedland said.

“This is more clear in the lung where the smoke is inhaled,” Freedland added. “However, the fact that prostate cancer death is linked with smoking means (these cancer causing) chemicals are not just present in the lungs but absorbed in the body and make their way to the prostate and, as such, they probably make their way into every organ in our body.”

SOURCE: bit.ly/2M2LqFg and bit.ly/2M0M6Ls JAMA Oncology, online May 24, 2018.