In many women, infection with certain types of human papillomavirus (HPV) is the first step in the progression from a normal cervix to cervical cancer. Recognized as the main cause of cervical cancer, sexually transmitted HPV induces the growth of abnormal cells that can become malignant.
Some experts feel that these changes are unlikely to progress to cancer in healthy women who don't smoke or have other cervical cancer risk factors.
It usually takes many years for cancer of the cervix to develop, but the process also can take place in less than 12 months. As cancer cells form, cells of abnormal size and shape appear on the surface of the cervix and begin to multiply.
Cervical dysplasia is the term used to describe the early growth of abnormal cells on the cervix that could progress to cancer. Cervical dysplasia is usually the first stage of cervical cancer, but women who have cervical dysplasia do not always develop cervical cancer.
"Dysplastic" cells look like cancer cells, but they are not considered malignant because they remain on the surface of the cervix and have not invaded healthy tissue.
Precancerous conditions are classified in three ways:
- CIN I - This classification involves mild dysplasia, in which abnormal cells are limited to the outer one-third of the surface cell layer (
epithelium) that lines the cervix. This classification includes cell changes caused by the human papillomavirus. It is common in young women and appears most often between the ages of 25 and 35.
- CIN II - This classification involves moderate dysplasia, in which abnormal cells make up about one-half of the thickness of the surface layer (epithelium).
- CIN III - This classification involves severe dysplasia, in which the entire thickness of the epithelium is composed of abnormal cells, but these cells have not yet spread below the surface. This category is also called carcinoma in situ. Severe dysplasia is most common in women between the ages of 30 and 40.
Without treatment, severely dysplastic cells are likely to penetrate deeper layers of the cervix and spread to other organs and tissues. This process, which may not occur until months or years after the abnormal cells first appear, is called invasive cervical cancer.
Pap Test Classification
The results of Pap tests are often classified by a method known as the Bethesda system. According to this system, the Pap report will state:
- Whether the sample is good or not (describing samples as either satisfactory, suboptimal, or unsatisfactory)
- Whether the results are normal or abnormal
Abnormal results are divided into three categories:
- Atypical squamous cells of undetermined significance (ASCUS)
- Low-grade squamous intraepithelial lesions (LGSIL)
- High-grade squamous intraepithelial lesions (HGSIL)
2. LGSIL. This category is used to describe Pap smears that show mild dysplasia. In mild dysplasia, abnormal cells are limited to the deepest one-third of the epithelium (surface cell layer) that lines the cervix. Also known as CIN I, this category includes cell changes caused by human papillomavirus (HPV).
- Moderate dysplasia (also known as CIN II), with abnormal cells making up about one-half of the thickness of the surface lining
- Severe dysplasia (also known as carcinoma in situ or CIN III), in which the entire thickness of the epithelium is composed of abnormal cells, but such cells have not yet spread below the surface.
For Further information about pap tests, go to Pap Smear.