Squamous Intraepithelial Lesion (SIL)

A squamous intraepithelial lesion (SIL) is an area or spot of skin on the inside or outside of your body that grows in a more disorganized way than the skin around it. These areas of skin can form on the lining of certain body parts, like your:

• Cervix
• Vagina
• Vulva
• Anus
• Penis
• Back of your throat

Skin that develops lesions found to be an SIL usually comes from a virus called the human papillomavirus, or HPV. The lesions themselves can’t be spread from person to person, but the HPV virus can transmit through sex as a sexually transmitted infection (STI).

The key characteristic of SILs is that the cell changes are limited to just the surface layer of skin. “Intraepithelial” means that the abnormal cells are present on the surface (epithelial tissue) of your cervix and have not grown past that surface layer.

SILs are precancers. This means they aren’t cancer, but they could become cancer later. Early detection is key to preventing SILs from progressing to cancer.

Low-grade vs. high-grade squamous intraepithelial lesions

Healthcare providers classify SILs as low-grade or high-grade:

• Low-grade (LSIL). Sometimes called mild dysplasia, these lesions only look slightly different under a microscope compared to normal skin. They can go away without treatment and are less likely to turn into cancer.
• High-grade (HSIL). High-grade SILs include moderate dysplasia, severe dysplasia and neoplasia in-situ (the last phase before tissue becomes cancerous). These lesions look very abnormal under a microscope. They usually need some form of treatment right away or they could turn into cancer.

What are the symptoms of squamous intraepithelial lesions?

SILs don’t usually cause symptoms. Most people find out they have it after a pelvic exam, Pap smear or anoscopy.

Let your healthcare provider know right away if you notice any of the following symptoms in your genital area:

• Abnormal discharge or bleeding
• Bumps or genital warts
• Burning
• Itching
• Pain
• Redness

SILs in the back of your throat may cause:

• Earaches
• Hoarseness
• Pain when swallowing
• Prolonged sore throat (pharyngitis)
• Swollen lymph nodes

Be sure to discuss how often you need cervical, vaginal or anal Pap smears. These screenings are the gold standard for detecting SILs on your genital area.

What causes squamous intraepithelial lesions?

Human papillomavirus (HPV) is the sexually transmitted infection (STI) that causes about 90% of all SILs. HPV causes some cells to grow faster and differently from the healthy cells around them.

There are over 100 different types of HPV infections, but the irregular cells that can lead to cancer usually come from HPV types 16 and 18. These are high-risk strains that tend to be responsible for a significant portion of high-grade SILs. But other high-risk strains like types 31, 33, 45, 52 and 58 can also contribute. Low-grade SILs tend to result from HPV types 6 and 11, but can also result from other types.

Your body’s immune system can fight off some types of HPV. But sometimes, it can’t fight it off completely, which means you can develop SIL over the course of many years without knowing it.

Who’s at risk for squamous intraepithelial lesions?

You’re at an increased risk for SIL if you:

• Have a suppressed immune system (immunocompromised) and HPV infection, which makes it harder for your body to fight the virus
• Smoke cigarettes and have HPV, as the chemicals in tobacco increase your risk of cell damage and weaken your immune system
• Practice unsafe sex, which may include having multiple sexual partners (vaginal, anal or oral sex) and having unprotected sex (like not using a condom)

What are the complications of SIL?

The biggest complication of SIL is that the cells could potentially progress to cancer. You can take steps to prevent this from happening by following your provider’s treatment plan and recommendations.

Your treatment plan may involve more frequent Pap tests to monitor cell changes. Or it might involve a procedure to remove the area of your skin with the irregular cells. Either way, you’ll want to be proactive in making sure SIL doesn’t progress.

Remember, an SIL doesn’t mean you have cancer.

How are squamous intraepithelial lesions diagnosed?

There are a variety of tests that healthcare providers use to screen for and diagnose SILs:

• Pap smears screen for cervical cancer. They can also help detect vulvar and vaginal cancers. Anal Pap smears test the anus for dysplasia and cancer.
• Colposcopy is a special type of examination for your cervix, vulva and vagina that your provider may use if a Pap smear shows SIL or evidence of the HPV virus.
• A biopsy, which involves your provider getting a tissue sample from your body to diagnose a precancer or cancer. For SIL involving your cervix, vagina or vulva, a biopsy can help your provider further analyze the cells. A throat exam helps your healthcare provider make a diagnosis of oropharyngeal cancer.

It’s important to note that SIL and cancer can take many years after an HPV infection to develop.

Is there routine screening for squamous intraepithelial lesions?

Out of all the HPV-related cancers, routine screening is only recommended for cervical cancer. The U.S. Preventive Services Task Force recommends routine cervical cancer screening for females beginning at 21. Based on your age, screening may include a Pap smear, an HPV test or both.

Talk to your healthcare provider about the right screening guidelines for your age and risk level. You may need more frequent screenings if you’ve tested positive for HPV or had abnormal Pap smears in the past.

What does negative for squamous intraepithelial lesion or malignancy mean?

A negative for squamous intraepithelial lesion, sometimes called NILM, means there are no irregular cells or signs of precancer on your Pap test. Even though this is a good result, you should still continue regular cervical cancer screenings at an interval your healthcare provider recommends.

Can you have low-grade squamous intraepithelial lesion (LSIL) without having HPV?

Yes. While HPV is the leading cause of all LSILs, up to 10% of people will test negative for HPV. This means you can have LSIL and not have HPV.

Does a high-grade squamous intraepithelial lesion mean I have HPV?

No. But HPV is the cause in up to 90% of all cases of HSIL. This means there’s a small chance something other than HPV causes HSIL.

How are squamous intraepithelial lesions treated?

Most low-grade lesions go away on their own. High-grade lesions require treatment. Depending on the location of the lesions, your healthcare provider may recommend:

• Topical treatments. You may apply some medicine directly to your skin. The creams or ointments may contain chemotherapy, hormones or substances to stimulate your immune system.
• Cryotherapy. Extreme cold, achieved with liquid nitrogen, can treat some lesions, such as anal or genital warts. Cryotherapy freezes away abnormal tissue.
• Laser treatment. A powerful laser uses light to burn away abnormal tissue.
• Excisional surgery. Your healthcare provider may recommend cutting the abnormal tissue out of your body. For SIL on your cervix, you may need a loop electrosurgical excision procedure (LEEP) or a cone biopsy.

How likely is cancer with high-grade squamous intraepithelial lesion?

An HSIL result on a Pap test doesn’t necessarily mean you have cancer. It means you have irregular cells on your cervix that could change into cancer. It doesn’t mean the cells automatically will change to cancerous cells. If the cells are left untreated, they progress to cancer in about 2% of all cases.

There’s also no telling how long it could take for the cells to change to cancer (if they do change). It could take 10 years or it could take 10 months. But with early detection and proper treatment, there’s a good chance it doesn’t progress to cancer at all.

How can I prevent squamous intraepithelial lesions?

The best way to prevent squamous intraepithelial lesions is by getting the HPV vaccine. It prevents up to 90% of HPV-related SILs. Talk to a healthcare provider about the vaccine to see if you’re eligible to get it.

Other ways to reduce your risk of HPV include:

• Practicing safe sex. Use condoms and dental dams.
• Limiting how many sexual partners you have.
• Being open with your partners about any STIs you have.
• Sticking to the screening guidelines that are right for your age and risk level. Your healthcare provider is the best person to help you determine how frequently you need a Pap smear.

What’s the outlook for people with squamous intraepithelial lesions?

Mild (low-grade) SIL usually goes away on its own. Moderate to severe (high-grade) SIL that’s treated early usually doesn’t turn into invasive cancer. Understanding your risk for cancer and following your healthcare provider’s recommendations (especially for future cancer screenings) is very important.

When should I see my healthcare provider?

Contact a healthcare provider if you notice any abnormal symptoms in your genitals, mouth or throat. You should also talk to a healthcare provider if you think you may have had genital contact with someone who has HPV.

Be sure to have a conversation with your healthcare provider about how frequently you should have Pap tests and other cancer screenings. These screenings have the potential to save lives because they can detect irregular cells before they progress.

What questions should I ask my provider about squamous intraepithelial lesions?

Questions you might want to ask your healthcare provider include:

• If I have an SIL, what are the chances of it turning into cancer?
• Should I get the HPV vaccine?
• Should I worry about the results of my Pap smear?
• Should I get more frequent Pap smears?
• What treatment do you recommend?
• What’s my risk of developing another SIL?