Low Grade Squamous Intraepithelial Lesion (LSIL) of the Cervix: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC and Zuzanna Gorski MD FRCPC
May 17, 2026

Low grade squamous intraepithelial lesion (LSIL) is a precancerous condition of the cervix caused by infection with human papillomavirus (HPV). It is composed of squamous cells infected and altered by the virus. These abnormal cells are usually found in the transformation zone, the part of the cervix where glandular cells are gradually replaced by squamous cells. Another name for LSIL in the cervix is cervical intraepithelial neoplasia 1 (CIN1).

LSIL is not cancer. In most people, the immune system clears the underlying HPV infection and the cells return to normal on their own. Only a small number of cases progress to a more advanced precancerous lesion called high grade squamous intraepithelial lesion (HSIL) or to cervical cancer. Although this article focuses on LSIL of the cervix, the same diagnosis can also occur in the vagina, vulva, anal canal, and peri-anal skin.

This article will help you understand the findings in your pathology report, what each term means, and why it matters for your care.

What causes LSIL?

LSIL is caused by infection with HPV, a very common virus that spreads through close contact, including sexual activity. Most HPV infections clear on their own within one to two years, but in some people the infection persists and causes changes in the squamous cells of the cervix.

There are many different types of HPV. LSIL can be caused by both low-risk HPV types (such as HPV6 and HPV11), which rarely lead to cancer, and high-risk HPV types (such as HPV16 and HPV18), which are more strongly linked to progression toward HSIL and cervical cancer. Several factors increase the risk of developing LSIL or of having an LSIL that persists rather than resolving:

Persistent HPV infection — Infections that last longer than one to two years are the most important risk factor.
A weakened immune system — Conditions such as HIV infection, organ transplantation, or long-term immunosuppressive therapy make it harder for the body to clear the virus.
Cigarette smoking — Smoking damages cervical cells and makes them more vulnerable to HPV-related changes.
Long-term use of oral contraceptives — Has been associated with a modestly increased risk in some studies.
Multiple sexual partners — Increases the chance of exposure to high-risk HPV types.
Lack of regular cervical screening — Without screening, abnormal cells can persist and progress before being detected.

What are the symptoms?

Most people with LSIL have no symptoms. The condition is usually detected during a routine cervical cancer screening test rather than because of any noticeable change. When symptoms do occur, they may include abnormal vaginal bleeding (such as bleeding after intercourse or between menstrual periods), an unusual vaginal discharge that may be watery or blood-tinged, or, less commonly, pelvic discomfort. Because LSIL often causes no symptoms, regular cervical screening remains the most reliable way to detect it.

How is the diagnosis made?

LSIL is most often first suspected when an abnormal Pap test or a positive HPV test identifies changes in the cells of the cervix. When this happens, the next step is typically a colposcopy, an examination of the cervix using a magnifying instrument called a colposcope. During colposcopy, a small tissue sample called a biopsy is taken from any abnormal area and sent to the laboratory. A separate sample may also be collected from inside the cervical canal using a procedure called endocervical curettage, which can detect abnormal cells that are not visible during colposcopy.

Under the microscope, a pathologist identifies LSIL by examining the extent to which the surface lining of the cervix has been replaced by abnormal squamous cells. In LSIL, the abnormal cells are confined to the lower one-third of this lining. To confirm the diagnosis and distinguish LSIL from HSIL and from other conditions that can look similar, the pathologist may perform a protein stain called p16, performed by immunohistochemistry. p16 staining is typically negative or only patchy in LSIL, in contrast to HSIL, where strong, continuous “block-type” p16 staining is the norm. HPV testing is also commonly performed to identify whether high-risk or low-risk HPV types are present, which helps guide the follow-up plan.

What does LSIL look like under the microscope?

Under the microscope, LSIL shows abnormal squamous cells confined to the lower one-third of the surface lining of the cervix. The cells remain in this layer and do not invade deeper tissue, which is what makes LSIL precancerous rather than cancer. Several features help the pathologist recognize LSIL:

Enlarged, darker cells — The abnormal cells are larger than normal, and the nucleus (the part of the cell that holds the genetic material) appears darker, with irregular or clumped chromatin.
Koilocytes — Koilocytes are squamous cells that have been infected by HPV. They have irregular dark nuclei and a clear space (or “halo”) around the nucleus, and they are a hallmark of LSIL.
Binucleated cells — Some cells contain two nuclei instead of one, another common feature of HPV infection.
Confinement to the lower epithelium — The abnormal cells stay in the lower one-third of the surface lining. The cells in the upper two-thirds appear mature and organized.
Negative or patchy p16 — In LSIL, the protein p16 is typically absent or shows only patchy staining, in contrast to the strong, continuous “block-type” staining seen in HSIL.

Surgical margins

Surgical margins are the cut edges of tissue removed during a surgical procedure, such as a loop electrosurgical excision procedure (LEEP) or cone biopsy. Margins are not usually assessed in LSIL because most people do not require surgical removal of the abnormal area. However, if LSIL is treated with an excisional procedure, the pathologist examines the margins under the microscope:

Negative margin — No LSIL cells are present at the cut edge of the tissue. This suggests the abnormal area was completely removed.
Positive margin — LSIL cells are present at the cut edge. This means some abnormal cells may remain, increasing the chance that LSIL recurs.

Margins are reported only on excision specimens. They are not reported on Pap tests or small biopsies, which are not intended to remove the entire lesion.

What is the prognosis?

The outlook for LSIL is generally very favorable. Most cases (approximately 60 to 70%) resolve on their own within two years, particularly in younger patients whose immune system clears the underlying HPV infection. Only a small minority progress to HSIL, and the progression from LSIL all the way to invasive cervical cancer is rare and typically requires HSIL as an intermediate step over many years.

Several factors influence the likelihood that LSIL will resolve, persist, or progress:

Age — Younger patients are more likely to clear the underlying HPV infection and have their LSIL resolve spontaneously.
HPV type — LSIL caused by low-risk HPV types (such as HPV6 or HPV11) very rarely progresses to cancer. LSIL caused by high-risk HPV types (such as HPV16 or HPV18) is more likely to persist or progress.
Persistent HPV infection — Across all age groups, persistence of high-risk HPV after the initial diagnosis is the most important predictor of progression.
Immune status — People with weakened immune systems (HIV infection, organ transplant, long-term immunosuppression) are at higher risk of LSIL persisting or progressing and may require closer surveillance.
Smoking — Continued smoking is associated with reduced clearance of HPV infection and a higher risk of LSIL persistence.

What happens after this diagnosis?

Because most LSIL resolves on its own, immediate treatment is usually not needed. The discussion between you and your doctor about next steps depends on your age, your HPV test results, and whether the LSIL was found on a Pap test alone or confirmed by biopsy.

Options the team may consider include:

Observation with repeat testing — The most common approach for LSIL is observation with repeat Pap testing or HPV testing, typically at 6 to 12 month intervals. Most LSILs that will resolve will do so during this time.
Colposcopy and biopsy — If colposcopy and biopsy have not already been done, your doctor may discuss them to confirm the diagnosis and rule out a more advanced lesion such as HSIL.
Closer monitoring for high-risk situations — When LSIL is associated with a high-risk HPV type, or when the patient is immunocompromised, the doctor may suggest more frequent monitoring during the first one to two years.
Treatment for persistent disease — If LSIL persists beyond 2 years, the team may discuss treatment options, including a loop electrosurgical excision procedure (LEEP), cone biopsy, or ablative procedures such as cryotherapy or laser therapy. Excisional procedures provide tissue for pathology examination and confirm the absence of underlying HSIL, while ablative procedures destroy the abnormal area but do not provide a specimen.

For patients under 25 years of age, observation with repeat testing is generally preferred over immediate intervention even if LSIL persists, because spontaneous resolution rates are high and procedures on the cervix in young patients can affect future pregnancies. Older patients with persistent LSIL or concerning features may be more likely to discuss excision.

Questions to ask your doctor

Was LSIL the only finding on my Pap test or biopsy?
Did my sample test positive for HPV, and if so, was it a low-risk or high-risk type?
Was p16 staining performed, and what did the result show?
What follow-up plan would you recommend for me based on my age and HPV results?
How often will I need Pap tests or HPV testing, and for how long?
At what point would you consider treatment instead of continued monitoring?
If treatment is needed, what are the options and how do they differ?
How do my smoking status, immune health, or medical history affect my risk of progression?
Should I consider HPV vaccination if I have not already been vaccinated?
Does this finding change anything about my plans for pregnancy or contraception?
What symptoms should I watch for between appointments?
When can I return to routine cervical cancer screening?