What is the difference between precancerous conditions and cancer of the cervix?

Cells on the surface of the cervix sometimes appear abnormal but not cancerous. Scientists believe that some abnormal changes in cells on the cervix are the first step in a series of slow changes that can lead to cancer years later. That is, some abnormal changes are precancerous, and they may become cancerous with time.

Over the years, doctors have used different terms to refer to abnormal changes in the cells on the surface of the cervix. One term now used is squamous intraepithelial lesion (SIL). (The word lesion refers to an area of abnormal tissue; intraepithelial means that the abnormal cells are present only in the surface layer of cells.) Changes in these cells can be divided into two categories:

Low-grade SIL (LGSIL) refers to early changes in the size, shape and number of cells that form the surface of the cervix. Some low-grade lesions go away on their own. However, with time, others may grow larger or become more abnormal, forming a high-grade lesion. Precancerous low-grade lesions also may be called mild dysplasia or cervical intraepithelial neoplasia 1 (CIN 1). Such early changes in the cervix most often occur in women between the ages of 25 and 35 but can appear in other age groups as well.

High-grade SIL (HGSIL) means that the precancerous changes are more severe; they look very different from normal cells. Like low-grade SIL, these precancerous changes involve only cells on the surface of the cervix. The cells will not become cancerous and invade deeper layers of the cervix for many months, perhaps years. Nevertheless, HGSIL on a Pap smear may be associated with malignancy of the cervix. Therefore, a proper diagnostic evaluation is necessary. This usually begins with a colposcopic evaluation of the cervix. High-grade lesions also may be called moderate or severe dysplasia, CIN 2 or 3, or carcinoma in situ. They develop most often in women between the ages of 30 and 40, but can occur at other ages as well.

If abnormal cells spread deeper into the cervix or to other tissues or organs, the disease is then called cervical cancer, or invasive cervical cancer. The average age of cervical cancer patients is 50.