20.3 Risk factors

Table 20.2 Risk factors for cervical cancer, by direction of association and strength of evidence


Increases risk

Decreases risk

Convincing or probable

Infection with "high-risk" types of genital human papilloma viruses (HPV)1,2

Infection with human immunodeficiency virus, type 1 (HIV-1)2

Tobacco smoking3

Oral contraceptives2,4

High parity5

Low socio-economic status6


1 "high-risk" HPV types include 16, 18, 31, 33, 35, 39, 45, 51, 56, 58, 59, 66; 2 International Agency for Research on Cancer, 2011b;

3 Secretan et al., 2009; 4 combined oestrogen-progestogen formulations; 5 Castellsagué and Muñoz, 2003; 6 Faggiano et al., 1997

Many strains of human papilloma viruses (HPV) infect the genital squamous epithelia. Some strains (known as "low-risk") cause genital warts while other strains (known as "high-risk") cause cervical cancer. The association between cervical cancer and these high-risk types of HPV infection is so strong that HPV is considered to be a necessary cause of the disease (Bosch et al., 2002). Infection with high-risk HPV is very common, and most women who have been sexually active will be infected at some time during their lifetime (Bosch et al., 2008). In most women infection causes no symptoms and clears naturally within a few months. However, some women become re-infected and the virus persists; susceptibility to persistent infections is thought to increase risk of developing cervical lesions. The factor most consistently associated with risk of genital HPV infection is number of sexual partners (Winer and Koutsky, 2004).

Infection with human immunodeficiency virus, type 1 (HIV-1) is also recognised to cause cervical cancer.

As regards other risk factors, there is a causal relationship between smoking and squamous cell cancer of the cervix, which persists after adjustment for HPV infection. In the relatively few studies of adenocarcinoma and adeno-squamous cell carcinoma, no relationship with smoking has been found (International Agency for Research on Cancer, 2004b). Cervical cancer risk is raised in women who have used combined oestrogen-progestogen oral contraceptives for at least five years. Risk falls with increasing time since last use, and after 10 years returns to background levels. Risk also increases with the number of children that a woman has had (parity).

Women of lower socio-economic status have raised cervical cancer risk. While partly a function of variations in exposure to risk factors (de Sanjosé et al., 1997), this also reflects social class differences in access to cervical smear tests or participation in organised screening programmes (Segnan, 1997).

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