by Jason Wasserman MD PhD FRCPC and Zuzanna Gorski MD FRCPC
February 5, 2025
Low grade squamous intraepithelial lesion (LSIL) is a precancerous condition of the cervix caused by human papillomavirus (HPV). It is made up of abnormal squamous cells that have been infected and changed by the virus. These cells are found in the transformation zone, a part of the cervix where normal glandular cells are gradually replaced by squamous cells.
In addition to the cervix, LSIL can also affect the vagina and vulva. In both women and men, LSIL may also involve the anal canal and peri-anal skin. Another name for LSIL is cervical intraepithelial neoplasia 1 (CIN1).
Although LSIL is considered a non-cancerous condition, there is a small risk that it will turn into a type of cervical cancer called HPV associated squamous cell carcinoma over time. However, for most people with LSIL, the immune system will remove the infected cells and the tissue will return to normal.
High grade squamous intraepithelial lesion (HSIL) is a related condition that is also caused by HPV. However, compared to LSIL, the risk of developing cancer from HSIL is much higher. Because LSIL has a lower risk of progressing, doctors usually recommend monitoring rather than immediate treatment.
Most people with LSIL do not have any symptoms, which is why it is often detected through routine Pap tests. However, in some cases, LSIL can cause:
Since LSIL is a precancerous condition, regular screening is important to monitor for any changes that could indicate a more advanced lesion, such as HSIL.
LSIL is caused by a persistent infection with low-risk or high-risk HPV. HPV is a common virus that spreads through direct person-to-person contact, including sexual contact. In most cases, the immune system clears the infection within a couple of years, but in some people, the virus stays in the cervix and leads to abnormal cell changes.
There are many different types of HPV, but LSIL is most often caused by low-risk HPV types such as HPV 6 and 11 or by high-risk types such as HPV 16 and 18. Unlike high-risk HPV infections, low-risk HPV infections rarely lead to cervical cancer.
The risk factors for developing LSIL include:
LSIL is usually first detected through a Pap test (Pap smear), a screening test that checks for abnormal squamous cells in the cervix. If LSIL is suspected, further tests may be needed to confirm the diagnosis:
If a biopsy confirms LSIL, most patients are monitored with repeat Pap tests rather than immediate treatment.
Under the microscope, LSIL consists of abnormal squamous cells that appear darker and larger than normal squamous cells. The genetic material (chromatin) inside the nucleus may look coarse or vesicular, meaning it is divided into small clusters.
Some of the abnormal cells may have two nuclei instead of one, a feature commonly seen in HPV-infected cells. These cells are called koilocytes, and they are a hallmark of HPV-related changes in the cervix.
Immunohistochemistry for p16 may also be performed. Unlike HSIL, the abnormal squamous cells in LSIL are typically negative or only weakly positive for p16.
Unlike HSIL, which requires immediate treatment, LSIL is often monitored with repeat Pap tests instead of surgery. This is because LSIL often goes away on its own, especially in young women.
Common management options include:
If LSIL is found on a Pap test, your doctor will monitor the cervix with repeat testing rather than immediate treatment.
Because LSIL has a low risk of turning into cancer, immediate surgery is usually not necessary. However, it is important to attend all follow-up visits to make sure LSIL does not progress.
A margin is the edge of the tissue that is removed during surgery. Margins are usually not a concern in LSIL, because most patients do not need surgical removal. However, in cases where LSIL is treated with LEEP, cone biopsy, or laser therapy, pathologists will examine the margins to ensure that all abnormal cells have been removed.
Margins are only described in surgical specimens. Pap smears and small biopsies do not have margins.