The cervix is the lower part of the uterus (womb). It is sometimes called the uterine cervix. The body (upper part) 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 exocervix (or ectocervix). The place where these 2 parts meet is called the transformation zone. Most cervical cancers start in the transformation zone.

Cervical cancers and cervical pre-cancers are classified by how they look under a microscope. There are 2 main types of cervical cancers: squamous cell carcinoma and adenocarcinoma. About 80% to 90% of cervical cancers are squamous cell carcinomas. These cancers are from 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. Squamous cell carcinomas most often begin where the exocervix 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.

Although cervical cancers start from cells with pre-cancerous changes (pre-cancers), only some of the women with precancers 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 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?"

Pre-cancerous changes are 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?"

Although almost all cervical cancers are either squamous cell carcinomas or adenocarcinomas, other types of cancer also can start in the cervix. These other types, such as melanoma, sarcoma, and lymphoma, occur more commonly in other parts of the body. This document discusses the more common cervical cancer types, and will not further discuss these rare types.