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"Basically we found that people who smoke had a higher risk of their tumor coming back, of it spreading and, ultimately, even dying of prostate cancer," said study co-author Dr. Michael Zelefsky. He is vice chair of clinical research in the department of radiation oncology at Memorial Sloan Kettering Cancer Center in New York City.
"But interestingly, this applied only to 'current smokers' who were smoking around the time they received external beam therapy," Zelefsky added, referring to the standard form of radiation treatment for prostate cancer. "Former smokers did not have the increased risk for disease spread and recurrence that current smokers did," he said.
"However, we also looked at how smoking affected treatment side effects," from the radiation treatment, which can include rectal bleeding and/or frequent and urgent urination, he noted. "And we saw that both patients who smoked and former smokers seemed to have a higher risk of urinary-related side effects after therapy."
Zelefsky and his colleagues reported the findings online Jan. 27 in the journal BJU International.
The research team pointed out that 19 percent of American adults smoke.
To explore the impact of smoking history on prostate cancer treatment and progression, the study authors focused on nearly 2,400 patients who underwent treatment for prostate cancer between 1988 and 2005.
Nearly 50 percent were identified as "former smokers," even if they had only kicked their habit shortly before beginning cancer treatment.
Disease progression, relapse, symptoms and deaths were all tracked for an average of eight years, as were all reactions to the radiation treatment.
The researchers determined that the likelihood of surviving prostate cancer for a decade without experiencing any disease recurrence was about 66 percent among patients who had never smoked. By comparison, that figure fell to 52 percent among patients who were current smokers.
Former smokers fared better than current smokers, with about 62 percent projected to hit the 10-year survival mark.
But compared with those who had never smoked, both current and former smokers faced a notably higher risk for the toxic urinary side effects that can occur with radiation treatment.
Zelefsky said the new study wasn't designed to highlight exactly how smoking worsens cancer prognosis. But he noted that one leading hypothesis is that smoking may reduce oxygen concentrations in the tumor region, perhaps making tumors less sensitive to radiation.
"We can't say for any certainty that this is the case," he said. "But what we can say, of course, is that smoking is not good for you. Clearly. We've long known that it increases the chances for developing lung cancer and cardiovascular disease. But this finding suggests that smoking may also undermine the battle against prostate cancer, and perhaps all cancers in general," Zelefsky said.
"So, at minimum this should make us more cognizant of the need to get a good smoking history on prostate cancer patients, and [to get] more proactive in terms of referring them for smoking cessation programs, rather than putting the issue on the backburner while undergoing treatment," he suggested.
Dr. Stephen Freedland, a professor of surgery at Cedars-Sinai Health System in Los Angeles, said the finding adds to growing evidence that smoking is associated with aggressive prostate cancer.
However, a cause-and-effect link was not proven in the new study.
"They clearly found that the risk of dying from prostate cancer goes up for smokers," Freedland said. "And, importantly, they controlled for the fact that smokers generally have other health problems in addition to cancer, and still found that smoking independently raises the risk of dying specifically from the cancer.
"So, I would say that quitting smoking is better than not quitting, and not starting in the first place is the best thing," he said. "But whichever is the case, it's not too late. If you're a smoker and you get prostate cancer, you should really consider that maybe it's time to stop."
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SOURCES: Michael Zelefsky, M.D., professor, radiation oncology, and vice chair, clinical research, department of radiation oncology, Memorial Sloan Kettering Cancer Center, New York City; Stephen Freedland, M.D., professor, surgery, Cedars-Sinai Health System, Los Angeles; Jan. 27, 2015, BJU International, online