The cervix is the lower part of the uterus (womb). It is sometimes called the uterine cervix. The body of the uterus (the upper part) is where a fetus grows. The cervix connects the body of the uterus to the vagina (birth canal). The part of the cervix closest to the body of the uterus is called the endocervix. The part next to the vagina is the exocervix (or ectocervix). The 2 main types of cells covering the cervix are squamous
cells (on the exocervix) and glandular cells (on the endocervix). The place where these 2 cell types meet is called the transformation zone. Most cervical cancers start in the transformation zone. Most cervical cancers begin in the cells lining the cervix. These cells do not suddenly change into cancer. Instead, the normal cells of the cervix gradually develop precancerous
changes that turn into cancer. Doctors use several terms to describe these precancerous 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 the section, "Can cervical cancer be prevented?").Cervical cancers and cervical pre-cancers are classified by how they look under a
microscope. There are 2 main types of cervical cancer: squamous cell carcinoma and
adenocarcinoma. About 80% to 90% of cervical cancers are squamous cell carcinomas.
These cancers start in the squamous cells that cover the surface of the exocervix. Under
the microscope, this type of cancer is made up of cells that are like squamous cells.
Most of the remaining cervical cancers are adenocarcinomas. Cervical adenocarcinomas
seem to have become more common in the last 20 to 30 years. Cervical adenocarcinoma
develops from the mucus-producing gland cells of the endocervix. Less commonly,
cervical cancers have features of both squamous cell carcinomas and adenocarcinomas.
These are called adenosquamous carcinomas or mixed carcinomas.
Although cervical cancers start from cells with pre-cancerous changes (pre-cancers), only
some women with pre-cancers of the cervix will develop cancer. The change from precancer
to cancer usually takes several years -- but it can happen in less than a year. For
most women, pre-cancerous cells will remain unchanged and go away without any
treatment. Still, in some women pre-cancers turn into true (invasive) cancers. Treating all
pre-cancers can prevent almost all true cancers. Pre-cancerous changes and specific types
of treatment for pre-cancers are discussed in the section, "Can cervical cancer be
prevented?"
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