The cervix is the lower part of the uterus (womb). The upper part, or body, of the uterus, 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 ectocervix. Most cervical cancers start where these 2 parts meet.
Cancer of the cervix (also known as cervical cancer) begins in the lining of the cervix. Cervical cancers do not form suddenly. Normal cervical cells 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.
There are 2 main types of cervical cancers: squamous cell carcinoma and adenocarcinoma. Cervical cancers and cervical precancers are classified by how they look under a microscope. About 80% to 90% of cervical cancers are squamous cell carcinomas, which are composed of cells that resemble the flat, thin cells called squamous cells that cover the surface of the endocervix. Squamous cell carcinomas most often begin where the ectocervix joins the endocervix.
The remaining 10% to 20% of cervical cancers are adenocarcinomas. Adenocarcinomas are becoming more common in women born 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.
Only some women with pre-cancerous changes of the cervix will develop cancer. This process usually takes several years but sometimes can happen in less than a year. For most women, pre-cancerous cells will remain unchanged and go away without any treatment. But if these precancers are treated, almost all true cancers can be prevented. Pre-cancerous changes and specific types of treatment for precancers are discussed in the section, "Can Cervical Cancer Be Prevented?"Precancerous changes can be separated into different categories based on how the cells of the cervix look under a microscope. These categories are discussed in the section, "Can Cervical Cancer Be Prevented?"