Cervical cancer refers to the abnormal, uncontrolled growth of cells in the cervix, the lower part of the uterus (womb) where it opens into the vagina.  When the cells of the cervix are infected with HPV, they may become abnormal and start to grow in an uncontrolled way.

Types of cervical cancer

The two main types of cervical cancer are:

• squamous cell cancer
• glandular cell cancer.

Squamous cell cancer is the most common form of cervical cancer (about 80 percent of cases).  Abnormal changes are found in the squamous cells of the transformation zone, where the vagina meets the cervix.  (See figure below)

Glandular cell cancer is found in the glandular cells, sometimes called columnar cells or endocervical cells, which line the cervical canal (about 15 percent of cases).  (See figure below)

Cervical cancer usually grows very slowly, taking 10 or more years to develop.  It starts when some cells on the surface of the cervix become abnormal.

These abnormal pre-cancerous cells may return to normal by themselves.  In a small number of cases, they may develop into cancer if not treated.

It is impossible to tell which abnormal pre-cancerous cells will return to normal and which may become cancer.  This is why all abnormal cells must be followed up.

If women have regular smear tests, there is a high chance that any abnormal pre-cancerous cells will be found and treated long before they develop into cancer.

What causes cervical cancer?

Cervical cancer is caused by certain types of HPV.  Of the nearly 200 types of HPV, about 40 infect the genital area, and about 15–20 of these high-risk types can cause abnormal cells, which may progress to cancer.  The 15 high-risk oncogenic (cancer-causing) types of HPV are: 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66, 68 and 73.

Genital HPV is spread by skin-to-skin contact during sexual intercourse with a person who has the virus.  Genital HPV is the most common sexually transmitted infection, affecting an estimated 80 percent of sexually active women at some point in their life and probably as many men.

Most women who get HPV (especially those under 30 years) will clear it in 6–24 months without even knowing they had it.  However, some will not clear their HPV and will develop a persistent infection.  Women who have a persistent infection with a high-risk type of HPV may go on to develop cervical cancer if not treated.