VOA常速英语:Smokers More Likely to Die from Prostate Cancer

Men who smoke cigarettes are more likely to die of prostate cancer, according to a new study. Smoking also increases the risk of a recurrence of the disease.

There are about 900,000 cases of prostate cancer annually, and each year the disease kills about a quarter-million people worldwide.

Harvard researchers analyzed the medical and smoking histories of about 5,300 men with prostate cancer.

"Overall, current smokers had a 61 percent increased risk of both dying of prostate cancer and having a recurrence [of] prostate cancer," says researcher Stacey Kenfield. "We also looked at the amounts that current smokers were smoking, and we did see an increase in prostate cancer mortality if you smoked more cigarettes."

The link between smoking and prostate cancer extends to former smokers. The risk declines the longer they go without smoking, and the less they smoked before they quit.

"Quitting smoking was beneficial. Men who quit for at least 10 years had prostate-specific mortality risks and recurrence risks that were very similar to people who had never smoked," says Kenfield.

Men who quit less than 10 years before diagnosis had higher risks, and the quitters who had been heavy smokers for many years had prostate cancer rates similar to current smokers.

Although the study did not look at why smokers are at a higher risk for prostate cancer, Kenfield says there are several possibilities, starting with the known carcinogens - cancer-causing chemicals - in cigarette smoke. Hormones could also play a role.

"Studies have found an association between current smoking and increased testosterone, which is known to stimulate prostate cancer growth. And other studies have shown that nicotine induces angiogenesis, or the formation of new blood vessels."

And those new blood vessels can feed the growth of tumors, including prostate cancer. 

Kenfield says smokers were also more likely to have a more aggressive form of prostate cancer at the time of diagnosis.