High grade squamous intraepithelial lesion (HSIL)
This article was last reviewed and updated on October 31, 2018
by Emily Goebel, MD FRCPC
High grade squamous intraepithelial lesion (HSIL) is a pre-cancerous disease that develops on the vulva.
HSIL is caused by a virus called human papillomavirus (HPV).
If left untreated, patients with high grade squamous intraepithelial lesion are at high risk for developing a cancer called squamous carcinoma.
The normal vulva
The vulva is the external part of the female genital tract. It forms the opening of the vagina and includes the mons pubis, labia majora, labia minora and clitoris. The vulva is composed of skin. The surface of the skin is called the epidermis and is made up of squamous cells. The tissue beneath the epidermis is called the dermis, it contains blood vessels and connective tissue.
What is high grade squamous intraepithelial lesion (HSIL)?
High grade squamous intraepithelial lesion (HSIL) is a pre-cancerous disease that develops in the vulva when the squamous cells become infected with a virus known as human papillomavirus (HPV).
HSIL is called a pre-cancerous disease because it can turn into an invasive cancer called squamous cell carcinoma. The cells in HSIL are abnormal and look almost identical to cancer cells, however, they are only seen in the epidermis. In squamous cell carcinoma, abnormal cells are seen in both the epidermis and the dermis.
High grade squamous intraepithelial lesion (HSIL) was previously called vulvar intraepithelial neoplasia (VIN2-3) and some reports may still use this name.
The diagnosis of HSIL is usually made after a small sample of tissue is removed in a procedure called a biopsy. The entire area of disease with then be completely in a larger surgical procedure called an excision or vulvectomy.
A margin is any tissue that needs to be cut by the surgeon in order to remove the tumour from your body. The margins will only be described in your report after the entire tumour has been removed.
A margin is considered positive when HSIL is seen at the cut edge of the tissue.
Why is this important? Finding HSIL at the margin is associated with an increased risk of the disease coming back after treatment.
Cells infected with high risk types of human papillomavirus (HPV) produce large amounts of a protein called p16. Your pathologist may perform a test called immunohistochemistry to look for p16 inside the abnormal cells. This will confirm the diagnosis of HSIL and rule out other conditions that can look like HSIL under the microscope.
Why is this important? Almost all cases of HSIL are positive or reactive for p16 which means your pathologist saw the p16 protein in the abnormal cells.