What Is Cervical Cancer?
Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?
Cervical cancer starts in the cells lining the cervix -- the lower part of the uterus (womb). This is sometimes called the uterine cervix. The fetus grows in the body of the uterus (the upper part). The cervix connects the body of the uterus to the vagina (birth canal).
The cervix has two different parts and is covered with two different types of cells.
The part of the cervix closest to the body of the uterus is called the endocervix and is covered with glandular cells.
The part next to the vagina is the exocervix (or ectocervix) and is covered in squamous cells.
These two cell types meet at a place called the transformation zone. The exact location of the transformation zone changes as you get older and if you give birth.
Most cervical cancers begin in the cells in the transformation zone. These cells do not suddenly change into cancer. Instead, the normal cells of the cervix first gradually develop pre-cancerous changes that turn into cancer. Doctors use several terms to describe these pre-cancerous changes, including cervical intraepithelial neoplasia (CIN), squamous intraepithelial lesion (SIL), and dysplasia. These changes can be detected by the Pap test and treated to prevent cancer from developing (see Can Cervical Cancer Be Prevented?).
Although cervical cancers start from cells with pre-cancerous changes (pre-cancers), only some of the women with pre-cancers of the cervix will develop cancer. It usually takes several years for cervical pre-cancer to change to cervical cancer, but it also can happen in less than a year. For most women, pre-cancerous cells will go away without any treatment. Still, in some women pre-cancers turn into true (invasive) cancers. Treating all cervical pre-cancers can prevent almost all cervical cancers. Pre-cancerous changes and specific types of treatment for pre-cancers are discussed in Cervical Cancer Prevention and Early Detection.
Types of cervical cancer
Cervical cancers and cervical pre-cancers are classified by how they look under a microscope. The main types of cervical cancers are squamous cell carcinoma and adenocarcinoma.
Most (up to 9 out of 10) cervical cancers are squamous cell carcinomas. These cancers develop from cells in the exocervix and the cancer cells have features of squamous cells under the microscope. Squamous cell carcinomas most often begin in the transformation zone (where the exocervix joins the endocervix).
Most of the other cervical cancers are adenocarcinomas. Adenocarcinomas are cancers that develop from gland cells. Cervical adenocarcinoma develops from the mucus-producing gland cells of the endocervix. Cervical adenocarcinomas seem to have become more common in the past 20 to 30 years.
Less commonly, cervical cancers have features of both squamous cell carcinomas and adenocarcinomas. These are called adenosquamous carcinomas or mixed carcinomas.
Although almost all cervical cancers are either squamous cell carcinomas or adenocarcinomas, other types of cancer also can develop in the cervix. These other types, such as melanoma, sarcoma, and lymphoma, occur more commonly in other parts of the body.