People who are exposed to secondhand smoke are more likely to develop oral cancers than their counterparts who don't have this exposure, a systematic review and meta-analysis suggests. Researchers examined data from five previously published studies with a total of 1,179 cases of oral cancer and 5,798 controls. The analysis included 3,452 people who had exposure to secondhand smoke and 3,525 who didn't. Overall, individuals with secondhand smoke exposure were significantly more likely to develop oral cancer (odds ratio 1.51), researchers report in Tobacco Control. "It is estimated that tobacco smoke could have more than 4,000 chemicals, and close to 70 of these have carcinogenic effects," said senior study author Luís Monteiro of the Instituto Universitário de Ciências da Saúde in Gandra, Portugal. "So, it is logical that tobacco smoke that is released by the combustion of tobacco products and by the exhaled smoke from smokers could act also as carcinogen on non-smoker individuals that inhale these gases," Monteiro said by email. Longer exposure to secondhand smoke also appeared to increase the risk of oral cancer. Compared to people without any exposure to secondhand smoke, individuals with exposure of more than 10 or 15 years had a more than doubled risk of oral cancer (OR 2.07). With secondhand smoke exposure of less than 10 or 15 years, the risk was lower, but still significantly greater than no exposure (OR 1.56). Researchers also looked at how the intensity of exposure to secondhand smoke influenced oral cancer risk. Compared to no exposure, the risk of oral cancer was lower for exposure of less than 2 or 3 hours daily (OR 1.65) than for more than 2 or 3 hours daily (OR 2.15). The researchers note that one limitation of the study is that they identified only a handful of studies to include in the meta-analysis. None of the included studies were high-quality, and many had a potential for recall bias to influence the results, the authors also point out. The environmental factors underlying cancer causes are inextricably linked, and these factors were not part of the study analysis, said Elyse Park, a professor of psychiatry and medicine at Harvard Medical School and Massachusetts General Hospital in Boston who wasn't involved in the study. "Smokers cluster in households and communities, so the cultural and community norms and environmental exposure and risk is shared," Park said by email. "Smokers are also disproportionately more likely to be of low socioeconomic status; so it is aligned that individuals who are exposed to secondhand smoke are as well." Even so, the results underscore that clinicians should consider secondhand smoke exposure as a modifiable risk factor for cancer, said Dr. Michael Ong, a professor at the David Geffen School of Medicine and the Fielding School of Public Health at the University of California Los Angeles. "As clinicians, we often neglect to ask patients about secondhand smoke exposure," Dr. Ong, who wasn't involved in the study, said by email. "However, secondhand smoke exposure has significant health risks, both from cancer risk as this study shows as well as other health risks, such as cardiovascular disease." —Lisa Rapaport Source
