title: Oral and oropharyngeal cancer and the role of sexual behaviour: a systematic review.
abstract: OBJECTIVE
  This systematic review identified and evaluated the evidence for the role of sexual behaviours in the development of oropharyngeal cancers (OPCs) and oral cavity cancers (OCCs).
  
  
  METHODS
  Following the PRISMA guidelines, we identified observational and interventional studies reporting associations between several different sexual behaviours and OPC or OCC. Study quality was assessed independently by two reviewers using a validated scoring system.
  
  
  RESULTS
  From 513 papers identified, 21, reporting on 20 studies, fulfilled the inclusion criteria. Two cohort studies were rated as moderate quality. The 18 case-control studies were rated as weak; nine comparing people with OPC or OCC to people without cancer, eight comparing HPV-positive to HPV-negative cancer patients and one comparing OPCs to other head and neck cancers. One study was a pooled analysis of seven of the included studies with some additional information. Twelve sexual behaviours were assessed and 69 associations reported. The studies differed in the comparisons made, the sexual behaviours assessed, and how these were reported and categorized, so no quantitative meta-analyses were appropriate. Most studies combined OPC and OCC. Several significantly increased risks were seen with a high number of lifetime sexual partners (nine studies) and with the practice of oral sex (five studies), although two studies found a significant negative association with OCC and ever performing oral sex. Two cohort studies of men and women in homosexual relationships found increases in oral cancer risk, and a cohort study of men married to women who had a history of cervical cancer also showed an increased risk of oral cancers. Results for other sexual behaviours were limited and inconsistent, and these included the following: younger age at first sexual intercourse, number of lifetime oral sex partners, the practice of oral-anal sex, the number of oral-anal sex partners, and ever performing anal sex. Only one study assessed casual sex, never or rare use of a condom and having a sexual partner with a history of genital warts, finding significant associations in the two former behaviours.
  
  
  CONCLUSIONS
  The current evidence for sexual behaviours being risk factors for oral and oropharyngeal cancer is limited and inconsistent. Evidence suggests that the number of sexual partners and performing oral sex are associated with a greater risk. Furthermore men whose partners have had cervical cancer may have an increased risk. More studies looking at OPC specifically will be useful to determine whether these behaviours are subsite-selective.
authors.affiliation: Department of Epidemiology and Biostatistics, School of Population Health, University of Auckland, Auckland, New Zealand.
authors.forename: James A
authors.initials: JA
authors.lastname: Chancellor
authors.affiliation: Department of Epidemiology and Biostatistics, School of Population Health, University of Auckland, Auckland, New Zealand.
authors.forename: Sally J
authors.initials: SJ
authors.lastname: Ioannides
authors.affiliation: Department of Epidemiology and Biostatistics, School of Population Health, University of Auckland, Auckland, New Zealand.
authors.forename: James M
authors.initials: JM
authors.lastname: Elwood
keywords: human papillomavirus; oral cancer; oral cavity cancer; oral sex; oropharyngeal cancer; review; sexual behaviour