by Jason Wasserman MD PhD FRCPC
March 22, 2022
High-grade squamous intraepithelial lesion (HSIL) is a pre-cancerous, sexually transmitted disease caused by infection with a virus called human papillomavirus (HPV). In addition to the cervix, HSIL commonly involves the vagina and vulva. In both women and men, HSIL may also involve the anal canal and peri-anal skin.
HSIL develops after the specialized squamous cells on the surface of the cervix become infected by the virus. Infected cells show an abnormal pattern of development called dysplasia. 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.
The diagnosis of HSIL is usually made after some cells are removed from the cervix during a Pap test or a biopsy. The diagnosis can also be made when part or all of the cervix is removed for another reason. The tissue sample is then sent to a pathologist who examines it under the microscope.
When examined under the microscope, the abnormal squamous cells in HSIL are darker and larger than the squamous cells normally found in the cervix. The chromatin (genetic material) which is found inside the nucleus of the cell may be described as coarse or vesicular which means it is divided into small groups. In a Pap smear, the abnormal squamous cells often form small groups but individual abnormal cells may also be seen.
When a larger tissue sample is removed in a biopsy or excision, the abnormal squamous cells will only be seen in the epithelium at the surface of the tissue. Unlike normal, healthy squamous cells, the abnormal cells do not become smaller and flatter as they move from the bottom of the epithelium to the top.
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. Almost all cases of HSIL are positive or reactive for p16 which means your pathologist saw the p16 protein in the abnormal cells.
After being diagnosed with HSIL your doctor should refer you to a specialist who will perform a colposcopy. A colposcopy allows your doctor to see the entire outer surface of the cervix. During the colposcopy, the doctor will be looking for any areas that look abnormal on the surface of the cervix. If an abnormality is found, the doctor may decide to take a small biopsy, to confirm the diagnosis of HSIL and to look for squamous cell carcinoma. Your doctor may also take a small sample of tissue from the endocervical canal and endometrium. All patients with HSIL should be followed closely or offered treatment to remove the disease. Talk to your doctor about the options available.
A margin is any tissue that has to be cut by the surgeon in order to remove the tumour from your body. If you underwent a surgical procedure such as an excision or resection to remove the entire tumour from your body, your pathologist will examine the margin closely to make sure there are no cancer cells at the cut edge of the tissue. A margin is considered positive when HSIL is seen at the edge of the cut tissue. Finding HSIL at the margin increases the risk that the tumour will grow back in that location.
The number and type of margins described in your report will depend on the type of procedure performed to remove the tumour from your body. Margins will not be described in your report after a Pap test or biopsy.
Typical margins include: