The cervix has two distinct areas: the inner, endocervix that leads into the uterus is made from glandular cells. The outer portion, called the ectocervix, leads to the vagina and is made from squamous cells. The portion of the cervix where these cells meet, called the transformation zone, is where most cervical cancers begin. Cervical cancers fall into two main types, depending on the cell type:
- Squamous cell carcinoma develops from the squamous cells of the transformation zone or the ectocervix. Most cervical cancers — nine out of 10 — are squamous cell carcinoma.
- Adenocarcinoma develops from the glandular cells of the cervix.
- Adenosquamous carcinoma or mixed carcinoma cervical cancers have cells that include both squamous and glandular cells. This “mixed” type of cervical cancer is uncommon.
Cervical cells can begin to grow abnormally when infection with the common human papillomavirus is present, and these abnormal changes in the cells, called either dysplasia, cervical epithelial neoplasia (CIN) or squamous intraepithelial lesion (SIL) are considered pre-cancers. Most often, the HPV infection will clear, and these changes resolve on their own. Only some of these pre-cancers become actual, invasive cervical cancer.
The progression from pre-cancer to cancer of the cervix is often slow, providing opportunity to detect the pre-cancer through routine screening and treat the condition before progression to invasive cancer. Cervical cancer screening involves the Pap test and/or the HPV test to detect human papillomavirus infection.
Progression can be faster in some women however, and an accurate diagnosis of the cervical cancer type is key to determining how aggressive treatment should be.