Secondhand smoke increases risk for oral cancer

There is a statistically significant association between secondhand smoke and the risk for oral cancer, researchers wrote in Tobacco Control.

“This is the first systematic review to answer this research question,” Saman Warnakulasuriya, BDS, PhD, DSc, a professor at King's College London and WHO Collaborating Centre for Oral Cancer, told Healio Primary Care.

Oral cancers — those of the lip, oral cavity and oropharynx — are responsible for 447,751 new cases of cancer and 228,389 deaths worldwide each year, according to 2018 estimates from the GLOBOCAN database. Major risk factors for oral cancer include smoking tobacco and using smokeless tobacco, drinking alcohol and chewing betel quid — a mixture of areca nut, tobacco, spices and other ingredients. Data from 192 countries show that about one-third of adult nonsmokers and 40% of children inhaled secondhand smoke during a 1-year period.

According to Warnakulasuriya, several of his patients who did not have the known risk factors were diagnosed with oral cancer. This prompted his research team to search “for evidence of whether [secondhand smoke] could be a factor for oral cancer, particularly in nonsmokers.”

They reviewed five case-control studies conducted from 2008 to 2019 — three from Asia, one from Europe and one conducted in North America and Europe — that included 1,179 cases and 5,798 controls. Secondhand smoke exposure was reported in 3,452 people.

According to the researchers, the overall OR for oral cancer among those exposed to secondhand smoke was 1.51 (95% CI, 1.2-1.91). In addition, individuals who were exposed to secondhand smoke for more than 10 or 15 years were at greater risk for oral cancer (OR = 2.07; 95% CI, 1.54-2.79) compared with nonexposed individuals. The findings were consistent across the studies, they added.

“We think the findings will come as a surprise to many as very little has been spoken on [secondhand smoke] as a possible etiological factor for oral cancer,” Warnakulasuriya said.

Multiple stakeholders can benefit from the findings, he said.

Physicians who have “a nonsmoker who is suspected of oral cancer, a family history of smoking or exposure to smoke at the workplace environment may be worth inquiry to establish the possible cause,” Warnakulasuriya said.

He added that for policy makers, the findings offer “additional support to enforce bans on smoking in enclosed environments [and] to society, to protect others from harm from exhaled and side stream smoke generated by smokers.”

References:

Ferlay J, et al. Int J Cancer. 2019;doi:10.1002/ijc.31937.

Mariano LC, et al. Tob Control. 2021;doi:10.1136/tobaccocontrol-2020-056393.