Cervical cancer starts with a change in the cellular DNA. DNA provides the cells with a basic set of instructions that regulate its growth, maturity, division and eventual death. A change in the DNA’s structure is known as a mutation. Once mutation occurs the cell repairing mechanism either repairs the damage or kills of the abnormal cell. In rare cases this cell may proliferate and create more abnormal cells. This gives rise to cancer.
Human Papilloma Virus
There is one most important cause of cervical cancer – infection with Human Papilloma virus (HPV). Almost all cases of cervical cancer occur in women who have been previously infected with the HPV. There are over 100 strains of HPV.
HPV spreads via unprotected sexual intercourse. HPV infection is very common and affects most sexually active women. At least a third of all women will develop a HPV infection within two years of starting to have regular sex.
However, most types of HPV do not cause any noticeable symptoms and the infection will pass without the need for treatment. Other types of HPV can cause genital warts.
Two types of HPV are known to have the highest risk of causing cervical cancer. These include HPV16 - which accounts for around 50-55% of all cases and HPV18 - which accounts for around 15-20% of all cases. There are 11 more types of HPV that have a higher chance of causing cancer.
These viruses contain genetic material that can be passed into the cells of the cervix. This then causes changes in the DNA of the cells of the cervix. These cells thus reproduce uncontrollably, leading to the growth of a cancerous tumour.
Before the cancer develops the cells in the cervix often show changes, known as cervical intraepithelial neoplasia (CIN). This is a pre-cancerous stage. These are not an immediate threat but may develop into ‘fully-blown’ cancer in the future. CIN is graded into three grades from one to three. The higher CIN 3, has the most abnormalities.
Risk factors for cervical cancer
Apart from HPV infection there are several cofactors that raise the risk of cervical cancer. These include:
Sexually active heterosexual women.
Women who have multiple sexual partners or have a promiscuous male sexual partner.
Smokers – women who smoke are twice as likely to get cervical cancer compared to non-smokers. This could be due to effects of tobacco and its chemicals on cervical cells.
Those with a weak immune system – this includes HIV positive patients and women after an organ transplant who are taking immunosuppressants to stop the body rejecting donated organs.
Oral contraceptive pills use for over 5 years may raise the risk of cervical cancer.
Women who have two children have twice the risk of getting cervical cancer compared to women who do not have any children. This is an unclear association. Some speculate that the hormonal changes that occur during pregnancy could make the cervix more vulnerable to the effects of HPV. Multiple pregnancies also raise the risk of cervical cancer.
Co-infections with HIV infection, Chlamydia infection.
Exposure to hormonal drug diethylstilbestrol (DES) raises the risk of vaginal and cervical cancer.
Those with a family history of cervical cancer are more at risk of getting this cancer. There is a possible genetic risk associated with HLA-B7.
There has not been any definitive evidence to support the claim that male circumcision prevents cervical cancer in their female sexual partners.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)