Study: Smoking during radiation therapy yields negative outcomes

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Tobacco smoking during radiation therapy for head-and-neck cancer is associated with unfavorable outcomes, said researchers from the department of radiation oncology at the University of California Davis Cancer Center in Sacramento, Calif., who evaluated the effect of continued cigarette smoking among patients undergoing radiation therapy.

The study, which was published April 15 in the International Journal of Radiation Oncology, Biology and Physics and led by Allen M. Chen, MD, reviewed the medical records of 101 patients with newly diagnosed squamous cell carcinoma of the head and neck who continued to smoke during radiation therapy.

Noting that there was a lack of tangible evidence to offer patients in convincing them to quit their habit during treatment, Chen said he wanted "concrete data to see if smoking was detrimental in terms of curability, overall survival and tolerability of treatment. We showed continued tobacco smoking contributed to negative outcomes with regard to all of those."

The researchers matched each active smoker to a control patient who had quit smoking before initiation of radiation therapy and pairing was based on tobacco history (pack-years), primary site, age, sex, Karnofsky Performance Status, disease stage, radiation dose, chemotherapy use, year of treatment and whether surgical resection was performed.

Outcomes were compared through the use of Kaplan-Meier analysis and normal tissue effects were graded according to the Radiation Therapy Oncology Group/European Organization for the Treatment of Cancer toxicity criteria, the authors wrote.

Chen and colleagues observed that active smokers had significantly lower five-year overall survival rates (23 percent compared to 55 percent), than those who had quit prior to radiation therapy after an average follow-up of 49 months.  In addition, locoregional control and disease-free survival rates where inferior for current smokers, at 58 percent vs. 69 percent and 42 percent vs. 65 percent, respectively.

The authors also noted that the differences held their statistical significance when patients treated by postoperative or definitive radiation therapy were analyzed separately. In addition, higher incidences of grade 3 or greater late complications were also significantly increased among active smokers, at 49 percent compared to 31 percent for former smokers.

The researchers believe that one reason that current smokers have poorer outcomes is due to smoking depriving the body of oxygen during radiation therapy, which requires oxygenation for the production of free radicals that attack cancer cells, they explained.  However, Chen and colleagues emphasized that while the findings are instructive for clinicians, further studies analyzing the biologic and molecular reasons underlying these differences are required.

Noted as limitations for the research, the authors wrote that the study was observational, and does not establish a cause-effect relationship between smoking during radiation therapy and poorer outcomes.  In addition, actual cause of death of each patient was not established and active smokers may be at higher risk of death from other medical problems, such as heart disease, stroke and diabetes.

"A diagnosis of cancer is emotionally devastating, and a lot of patients are reluctant to entertain the idea of smoking cessation,” said Chen. “Many patients can't or won't connect the dots, and, unfortunately, our data shows that by continuing to smoke, they are more likely to gamble away the possibility of cure.”