The Pap Smear and Cervical Cancer
Cervical cancer can develop from one of the two types of cells that line the outside of the cervix: squamous and columnar epithelial cells. Most cases result from cancers of the squamous layer, which are referred to as squamous cell carcinomas; the remaining types come from the columnar cells and are called adenocarcinomas. Almost all cases of cervical cancer are associated with the human papilloma virus (HPV). Specific strains, namely 16, 18, and 31, cause the majority of all cervical cancer cases.
Diagnosis of cervical cancer starts with a pap smear. There are several different results that come back from a pap smear. They are “normal”, “atypical squamous cells of undetermined significance” (ASC-US), “atypical squamous cells cannot rule out high grade lesion” (ASC-H), “low grade squamous intraepithelial lesion” (LSIL), and “high grade squamous intraepithelial lesion” (HSIL).
If a pap smear comes back as abnormal, than “reflex” HPV testing is done to determine if the specimen is infected with one of the cancer causing strains. All patients with ASC-H, LSIL, and HSIL undergo colposcopy (ie: direct visualization of the cervix for abnormalities). If ASC-US reflex HPV testing comes back negative (ie: no cancer causing strains) then routine pap smear screening is resumed. If the patient was ASC-US positive, and HPV testing comes back as positive then she would also undergo colposcopy.
Colposcopy allows direct visualization of the cervix for potential biopsy of abnormal areas. The results of the biopsy give a tissue diagnosis. They are recorded in grades depending on how “bad” the tissue looks. The possible results are cervical intraepithelial neoplasia (CIN) grades 1 through 3, or cancer. CIN grades refer to how dysplastic (ie: pre-cancerous) the tissue is. It is important to note that CIN refers to pre-cancer. The degree of dysplasia has important ramifications for treatment.