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Causal link reported between second-hand smoke and oral cancer

By Melanie Hinze
A causal link has been identified between exposure to second-hand tobacco smoke and oral cancer, according to research published in Tobacco Control.

The international team of researchers found that people exposed to second-hand tobacco smoke had a 51% increased risk of oral cancer.

Although it has been known for some time that smoking causes oral cancers, this new research aimed to investigate the previously unknown link with second-hand smoke only.

The researchers sourced studies published up to May 2020 from the PubMed, Web of Science, Scopus, Cochrane Library, Open Grey, and ProQuest databases, and conducted a systematic review and meta­-analysis of the five eligible studies.

In total, 6977 people were included, of which 1179 developed oral cancer and 5789 were controls. Among the participants, 3452 had been exposed to second-hand smoke, while 3525 had not.

People who had been exposed to second­-hand smoke for more than 10 or 15 years had more than double the risk of develop­ing oral cancer compared with those who had never been exposed. The study authors said this further supported the causal inference.

Professor Camile Farah, Director of the Australian Centre for Oral Oncology Research & Education, Perth, said that although the analysis centred on a small number of available studies, the results did appear to suggest a causal relationship between second-hand smoke and onset of oral cancer.

‘This study may go some way in explaining the higher number of oral cancer cases with no known history of smoking particularly seen in younger patients,’ added Professor Farah, who is an oral physician and maxillofacial pathologist with a particular interest in head and neck cancer.

‘Over the past 20 years, there has been a steady increase in oral cancer cases in those under the age of 40, with reasons for this increase still to be deter­mined,’ he said, noting that more research into the impact of second-hand smoke in better defined populations may assist.
Tob Control 2021; doi:10.1136/tobaccocontrol-2020-056393.