The link between the number of sexual partners a person has had and their risk of developing throat cancer has been reaffirmed by new research.
Mouth and throat tumours are sometimes linked to “high-risk” variants of the human papillomavirus (HPV), which can spread via oral sex.
The virus infects cells, occasionally causing them to become cancerous, sometimes over several decades.
While nine out of 10 people clear the infection naturally within two years, a third of throat cancer cases in the UK are linked to HPV, which is responsible for nearly all incidents in younger people.
To better understand the risk, scientists from Johns Hopkins University analysed 163 people with HPV-related throat cancer, as well as 345 individuals who did not have the disease.
Results suggest having more than 10 sexual partners raises a person’s risk of developing throat cancer by over four times.
The scientists also found having oral sex for the first time at under 18 was linked to an 80% higher risk of a later diagnosis, compared to those who became intimate when aged over 20.
Oral sex intensity, defined as a high number of partners across more than five years, also more than doubled a participant’s risk of the disease.
“Our study builds on previous research to demonstrate it is not only the number of oral sexual partners, but also other factors not previously appreciated that contribute to the risk of exposure to HPV orally and subsequent HPV-related oropharyngeal cancer,” study author said Dr Virginia Drake.
“As the incidence of HPV-related oropharyngeal cancer continues to rise in the United States, our study offers a contemporary evaluation of risk factors for this disease.
“We have uncovered additional nuances of how and why some people may develop this cancer, which may help identify those at greater risk.”
Mouth and throat cancers – also known as head and neck tumours – affect around 12,000 new people every year in the UK.
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The Johns Hopkins participants completed a behavioural survey between 2013 and 2018.
The results – published in the American Cancer Society journal Cancer – suggest a person’s number of sexual partners, age at first oral sex experience and the “intensity” of their encounters all raise their risk of developing oropharyngeal cancer.
Oropharyngeal cancer affects the middle part of the throat, just behind the mouth.
Having an “older” partner when the participant was “younger” was also linked to a 70% increased risk of a diagnosis. The scientists did not specify what ages these individuals were.
“Having a partner who had extramarital sex” raised the odds by 60%, the results show.
“Number of oral sex partners remains a strong risk factor for HPV‐OPC [HPV-related oropharyngeal cancer]; however, timing and intensity of oral sex are novel independent risk factors,” wrote the scientists.
“These behaviours suggest additional nuances of how and why some individuals develop HPV‐OPC.”
Does oral sex raise the risk of throat and mouth cancer?
Smoking and drinking excessive amounts of alcohol are the main risk factors for throat and mouth cancer, which include tumours of the lips, tongue and voice box.
Around a quarter of mouth cancers and a third of throat cancers in the UK are HPV-related, but detecting the virus in a patient does not necessarily mean the infection caused their disease.
There are more than 100 HPV variants, of which around 15 are associated with cancer.
As well as oral sex, these high-risk variants can be transmitted via vaginal and anal intercourse, raising the risk of cancer of the cervix, anus and penis.
Some lower-risk variants spread through skin-to-skin contact, causing genital warts.
The prevalence of HPV in the mouth is unclear.
A 2009/10 US study found one in 10 men and less than two in 50 women had HPV in their mouth.
A 2017 US study later found six in 100 men and one in 100 women carried potentially cancer-causing HPV variants in their mouth.
Of these individuals, just seven in 1,000 men and two in 1,000 women developed throat or mouth cancer.
There is very little research suggesting giving oral sex to a man or woman is more dangerous.
HPV-related oropharyngeal cancer is twice as common in men than women, particularly heterosexual males in their 40s and 50s.
This may suggest giving oral sex to a woman is more risky than giving it to a man.
The “concentration of HPV in the thinner, moist skin of a woman’s genitals is much higher than the amount in the thicker, dry skin of the penis”, which could affect how easily the virus gets passed on, according to the NHS.
Men and women may vary in their sexual behaviours, however, like their number of partners.
Oral sex can be made safer by a man wearing a condom or a woman placing a “dam” – “square of very thin, soft plastic” – across her genitals, acting as a barrier against infection.
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