Since 1993 cervical cancer has been classified as an AIDS-defining illness. At the time this was quite controversial as some doctors argued that HIV-positive women were no more likely to develop cervical cancer than HIV-negative women.

However, since effective HIV treatment became available, it has become clear that there is a small increase in the risk of cervical cancer developing in HIV-positive women.

The development of cervical cancer is linked to cell changes caused by some strains of the human papillomavirus (HPV), a virus that is also associated with genital warts.

It is worth emphasising that the reason the small increase in the number of cases of cervical cancer in HIV-positive women has been noticed is likely to be that women with HIV are living longer. Anti-HIV drugs do not cause cervical cancer.

Often the immune system successfully clears infection with HPV. HIV treatment does not have a direct effect against HPV. However HIV treatment does improve the ability of the immune system to fight infections, including HPV.

Human papillomavirus (HPV), is the underlying cause of cervical cancer. Infection with HPV is very common and is quite widespread amongst women with HIV. There are many different strains of HPV and only a few of these appear to cause cancer. Some strains of HPV cause visible, cauliflower-like warts on the genitals, but these are not the strains associated with cervical cancer.

In most cases, the body is able to clear infection with HPV, even of those strains that could cause cancer. However, HIV-positive women, particularly if they have a weak immune system, are less likely to be able to clear HPV infection naturally. Nevertheless, it is worth noting that even if high-risk strains of HPV persist, they usually do not cause cancer.

Women who became sexually active at a very young age or who have had many sexual partners have a higher risk of being infected with high-risk strains of HPV.

There is also some evidence that smoking increases the risk of cervical cancer if you are infected with high-risk strains of HPV.

Before cervical cancer develops, cells in the cervix go through a number of changes over many years. These pre-cancerous lesions are often called CIN (cervical intraepithelial neoplasia). They are graded according to their stage – CIN I, CIN II, and CIN III.

Cervical screening tests (often called Pap smears) can detect pre-cancerous changes to cells in the cervix before cancer develops. The test involves taking a sample of cells from the lining of the cervix. In the UK all women between the ages of 20 and 64 are recommended to have regular cervical screening.

Women with HIV are advised to have screening more frequently than other women. HIV-positive women should have a cervical smear when they are first diagnosed with HIV, six months after this, and then every year.

The cervix can be examined in more detail using a magnifying instrument called a colposcopy. At the same time small samples of tissue can be removed and examined under a microscope to see if pre-cancerous changes in the cells have occurred.

Symptoms of changes to cells in the cervix include bleeding after sex, bleeding between periods and an unusual discharge from the vagina. However, these symptoms usually do not appear until there are pre-cancerous changes, or even until the cancer is well-developed, so regular cervical screening is strongly recommended.

The earlier the treatment is provided the better, and if caught early the treatment of pre-cancerous changes in the cervix can be highly successful.

Pre-cancerous lesions can be treated by non-surgical means such as freezing with liquid nitrogen or laser treatment. There are also simple surgical procedures that involve removing a layer of pre-cancerous cells.

If the lesions are more advanced or cancer develops it is likely that surgery will be combined with local radiotherapy and chemotherapy. There is some evidence that women who take HIV treatment after treatment for pre-cancerous cervical changes or cervical cancer and have an undetectable viral load are less likely to develop a recurrence of the condition.

Two vaccines have been approved that provide some protection against the strains of HPV that are associated with the highest risk of cervical cancer.  NHS guidance suggests that one of these should be provided to girls before they are sexually active. Clinical trials are underway to see how safe and effective one of the vaccines is in women with HIV.