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The uterus is a pear shaped organ located in the lower abdomen between the bladder and the rectum. The cervix is the narrow opening at the base of the uterus, which leads into the vagina and out of the body. Above the uterus on each side are the fallopian tubes and ovaries. Together, the uterus, vagina, ovaries, and fallopian tubes make up the female reproductive system.

The cervix contains two kinds of cells: rectangular columnar cells and flat squamous cells. Columnar cells are constantly changing into squamous cells in an area of the cervix called the transitional zone. This is the most common place on the cervix for abnormal cells to develop. Most (85-90%) invasive cervical cancer develops this area and is called squamous cell carcinoma. Approximately 10-15% of cases of cervical cancer develop in glandular surface cells, called adenocarcinoma. In a third type of cervical cancer, which is very rare, called adenosquamous carcinoma, the abnormal cells have features that resemble both squamous cells and adenocarcinoma cells

The location of the transitional zone varies among women. In teenage girls, the transitional zone is on the immature cervix's outer surface and is more susceptible to infection than in adult women. In older women, the transitional zone may be located higher within the cervical canal.