"Radiation therapy requires oxygenation for the production of free radicals, which attack cancer cells," he said.

He also emphasized that their findings are based on an observational study, which does not establish a cause-effect relationship between smoking during radiation therapy and poorer outcomes. For instance, they were unable to determine with certainty the actual cause of death of each patient, and active smokers may be at higher risk of death from other medical problems such as heart disease, stroke and diabetes.

"Patients unable to quit may also have non-cancer-related medical and psychosocial problems that could possible contribute to inferior survival," Chen said.

"Those who continue to smoke even after a diagnosis of head and neck cancer are likely to be at higher risk for alcohol abuse, have less social support and have lifestyles associated with high-risk health behaviors. A diagnosis of cancer is emotionally devastating, and a lot of patients are reluctant to entertain the idea of smoking cessation. Many patients can't or won't connect the dots, and unfortunately, our data is showing that by continuing to smoke, they are more likely to gamble away the possibility of cure."

SOURCE American Society for Radiation Oncology