atypical squamous cell

Atypical squamous cells - ASC represent cellular abnormalities more marked than simple reactive changes, but which do not meet the criteria for squamous intraepithelial neoplasia (SIL). These cells are not of typical appearance and are, therefore, atypical.

The Pap diagnosis of Atypical Squamous Cells (ASC) is the most common abnormal finding during cervical cancer screening and is reported in about 5 percent of all cervical screening tests.

There are two subtypes of ASC:

 Atypical Squamous Cells of Undetermined Significance (ASC-US)
 Atypical Squamous Cells, Cannot Rule Out High-Grade Squamous Intra-epithelial Lesion (ASC-H).

Most nuclear enlargement in Pap tests is due to reactive change, and reactive changes and LSIL must be excluded by the pathologist when an ASC-US diagnosis is provided.

ASC-US results initiate reflex HPV testing, with positive HR HPV test results prompting colposcopic examination. ASC-US is the most common of the ASC diagnoses.

Since a high grade squamous intraepithelial lesion (HSIL) cannot be excluded in ASC-H, triage directly to colposcopy is recommended by the ASCCP for ASC-H diagnosis. ASC-H is rare.

For a diagnosis of ASC-H, the cytopathologist must first exclude moderate/severe cervical intraepithelial neoplasia or carcinoma in-situ (CIN3/HSIL).

In some cases, women having ASC-H findings may harbor HSIL or invasive cervical cancer in their follow up.

Of all women with HSIL results, 2% or less have invasive cervical cancer at the time of diagnosis. About 20% can however, progress to have invasive cervical cancer if not treated or followed appropriately.

Relative risk for ASC-H Pap diagnosis is certainly less than 20%, but HSIL must first be excluded by colposcopy and biopsy after ASC-H findings.

If no colposcopic lesion is visible in follow up of ASC-H, vigorous ECC should be undertaken.