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Secondhand smoke exposure and oral cancer risk: a systematic review and meta-analysis
  1. Lorena C. Mariano1,
  2. Saman Warnakulasuryia2,
  3. Kurt Straif3,4,
  4. Luís Monteiro1,5
  1. 1CESPU, Instituto de Investigação e Formação Avançada em Ciências e Tecnologias da Saúde (IINFACTS), Instituto Universitário de Ciências da Saúde (IUCS), Gandra, Portugal
  2. 2King's College London and WHO Collaborating Centre for Oral Cancer, London, UK
  3. 3ISGlobal Barcelona, Barcelona, Spain
  4. 4The Schiller Institute, Boston College, Chestnut Hill, MA, USA
  5. 5Medicine and Oral Surgery Department, Instituto Universitário de Ciências da Saúde (IUCS), Gandra, Portugal
  1. Correspondence to Dr Luís Monteiro, CESPU, Instituto de Investigação e Formação Avançada em Ciências e Tecnologias da Saúde (IINFACTS), Cancer Research Unit, Instituto Universitário de Ciências da Saúde (IUCS), Rua Central de Gandra, 1317, 4585 Gandra, Portugal; luis.monteiro{at}


Objectives Inhalation of secondhand smoke (SHS) causes several diseases, including lung cancer. Tobacco smoking is a known cause of oral cancer; however, it has not been established whether SHS also causes oral cancer . The aim of this study was to evaluate the potential association between SHS exposure and the risk of oral cancer.

Methods A systematic review and meta-analysis study (following the PRISMA guidelines) was developed to examine the studies reporting on the associations of SHS and the risk of oral cancer, employing a search strategy on electronic databases (PubMed, Web of Science, Scopus, Cochrane Library, Open Grey, and ProQuest databases for dissertations) until 10 May 2020. Meta-analyses and sensitivity analyses were performed using random-effect models. The protocol was registered in PROSPERO (CRD42020189970).

Results Following the application of eligibility criteria, five studies were included, comprising a total of 1179 cases and 5798 controls, with 3452 individuals exposed and 3525 individuals not exposed to SHS. An overall OR of 1.51 (95% CI 1.2o to 1.91, p=0.0004) for oral cancer was observed, without significant heterogeneity (I2=0%, p=0.41). The duration of exposure of more than 10 or 15 years increased the risk of oral cancer (OR 2.07, 95% CI 1.54 to 2.79, p<0.00001), compared with non-exposed individuals, without significant heterogeneity (I2=0%, p=0.76).

Conclusions This systematic review and meta-analysis supports a causal association between SHS exposure and oral cancer. Our results could provide guidance to public health professionals, researchers, and policymakers to further support effective SHS exposure prevention programs worldwide.

  • secondhand smoke
  • prevention
  • global health
  • environment

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  • Contributors LM, SW, and LSM conceived and designed the study. The search, selection, and quality of studies evaluation was performed by LM, SW, and LSM. Analysis and interpretation of the data was performed by all authors. All authors contributed to the manuscript development. All authors approved the final version of the manuscript for submission.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data are available in a public, open access repository. Data sharing not applicable as no datasets generated and/or analysed for this study. Data are available upon reasonable request. Additional information is provided in supplemental documents.

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