Cervical Cancer Risk Factors

The risk of a woman acquiring cervical cancer in her lifetime is measured through the assessment of the acquisition and potential persistence of oncogenic HPV infection. The possibility of infection with oncogenic HPV starts with the onset of sexual activity and lasts throughout a woman’s sexually active life (Gravitt and Jamshidi 2005).

Oncogenic HPV infection is the necessary cause of cervical cancer, but a number of other co-factors also appear to play a role too (McIntosh 2000; Franco et al 2001; Burd 2003):

• young age at first sexual experience
  
• other co-factors including:
  
  • cigarette smoking
    
  • long-term use of oral contraceptives
    
  • sexual behaviour (number of partners)
    
  • high number of pregnancies
    
  • other sexually transmitted infections (eg, HIV, chlamydia)
    
  • decreased or compromised immune response.

Cervical cancer risk co-factors: age of first sexual experience

It is known that the prevalence of HPV infection is greatest in women aged less than 25 years of age (Burk et al 1996; Baseman and Koutsky 2005) and in one study the peak in young women was associated with oncogenic HPV types (Herrero et al 2000; Baseman and Koutsky 2005). Although cervical cancer can take years to develop, the younger a woman is when she acquires the oncogenic virus, the greater the risk and the younger she may be when she develops cervical cancer.

Adolescent girls are particularly vulnerable to oncogenic HPV infection and its consequences, because infections contracted earlier in life have a higher risk of evolving unfavourably. Abnormalities may also develop more rapidly when cervical cells are in the early stages of maturity, but progression to a more severe state is rare (Szarewski and Sasieni 2004). Most, if not all, screening programmes do not include this age group of females (in some countries, none under 25 years old) as screening is not efficient in detecting changes in this young population due to developmental changes that are still taking place.

(Reference: Biswas et al 1997)

The increased probability of cervical cancer for women with an early sexual debut is substantial (Biswas et al 1997). The co-factors associated with cervical cancer were assessed in a study that included 134 Indian women with invasive cervical cancer and 134 control subjects. Younger age at first sexual intercourse was associated with a significantly increased risk of developing cervical cancer. (Biswas et al 1997).

Adenocarcinoma, a form of cervical cancer which can be harder to detect during screening unless an appropriate brush or similar instrument is used, may account for up to 20% of cervical cancer cases (Duarte-Franco and Franco 2004), and the incidence is increasing (Alfsen et al 2000; Smith et al 2000; Sheets 2002).


Cervical cancer: additional co-factors

Persistent oncogenic HPV infection is the necessary cause of cervical cancer, but additional co-factors also appear to be important (Franco et al 2001; Burd 2003; McIntosh 2000; Hildesheim et al 2001).

• Cigarette smoking: cervical cancer may develop more readily in smokers as the toxins in cigarettes concentrate in the cervical mucus. As well as having a direct oncogenic effect, smoking decreases local immune resistance. As a result, once infected, sexually active women who smoke are more likely to develop persistent HPV infection, which in turn increases the possibility of developing cervical cancer.
  
• Long-term use of oral contraceptives: this has been linked to an increased likelihood of developing cervical cancer. Epidemiological studies have found a correlation between cervical neoplasia and long-term (more than 5 years’) use of oral contraceptives.(Castellsagué and Muñoz 2003; Hellberg and Stendahl 2005).
  
• High number of pregnancies: women who have had a high number of live births are more likely to develop cervical cancer. The reason has not yet been fully established (Hinkula et al 2004).
  
• Other sexually transmitted infections (eg, HSV, chlamydia) (Bosch et al 2002): Research suggests that women with a history of infection with Chlamydia were more likely to develop cervical cancer, possibly mediated by inflammatory cytokine responses or independent effects on the female reproductive system including the cervix (Beatty et al 1994).

(Reference: Castellsagué and Muñoz 2003)

• Sexual behaviour: increasing numbers of sexual partners provides the opportunity for more HPV transmission to occur between partners (Bosch et al 2002).
  
• Decreased immunity: Immunocompromised individuals, such as those infected with human immunodeficiency virus, are more likely to develop HPV-associated anogenital cancers than age-matched healthy subjects (Palefsky and Holly 2003)