High grade squamous intraepithelial lesion (HSIL)

By Jason Wasserman MD PhD FRCPC
February 7, 2023

What is a high grade squamous intraepithelial lesion?

High grade squamous intraepithelial lesion (HSIL) is a precancerous condition that forms on the surface of certain organs such as the cervix, penis, vagina, vulva, and anal canal.

What causes high grade squamous intraepithelial lesion?

HSIL is caused by human papillomavirus (HPV). HSIL develops after specialized squamous cells found on the surface of the cervix, vagina, vulva, or anal canal become infected by the virus. Over time the infected cells develop genetic changes which lead to HSIL. There are many types of HPV but most cases of HSIL are caused by the high-risk types 16 and 18.

Is high grade squamous intraepithelial lesion a type of cancer?

HSIL is not cancer although patients with HSIL are at increased risk for developing a type of cancer called squamous cell carcinoma. For this reason, most patients with HSIL are offered treatment to remove the area of abnormal tissue. Low-grade squamous intraepithelial lesion (LSIL) is a related condition that is also caused by HPV. However, compared to HSIL, the risk of developing cancer from LSIL is much lower.

How is the diagnosis of high grade squamous intraepithelial lesion made?

The diagnosis is made after a Pap smear or biopsy is performed and the tissue is sent to a pathologist for examination under the microscope. Compared to normal, healthy squamous cells, the squamous cells in HSIL are larger and darker. Pathologists often describe these cells as hyperchromatic. When a test called immunohistochemistry is performed, the abnormal squamous cells produce large amounts of a protein called p16.