What Is a High-Grade Squamous Intraepithelial Lesion?

A high-grade squamous intraepithelial lesion, or HSIL, is a patch of clearly abnormal cells on the surface lining of the cervix. It is a precancer, not cancer, because the abnormal cells have not grown beneath the surface layer. Almost all HSIL is caused by a long-lasting infection with high-risk types of HPV, the common sexually transmitted virus. The result is a warning that arrives years ahead of any cancer, and it is highly treatable when screening finds it.

What the Words on Your Report Mean

HSIL replaced three older names: moderate dysplasia, severe dysplasia and carcinoma in situ.¹ On a biopsy report, the same change is often written as CIN2 (moderate) or CIN3 (severe, including carcinoma in situ).² “Squamous” refers to the flat, skin-like cells that line the outer cervix, and “intraepithelial” means the change stays within that surface layer. “Carcinoma in situ” sounds like cancer, but it still means the cells have not invaded deeper tissue.

On a Pap report, HSIL sits above two other labels. LSIL means low-grade changes, which often clear on their own. ASC-H means the cells look worrying but not clearly high-grade, so doctors check further. HSIL gets the most active follow-up of the three.

A Pap test and a biopsy answer different questions. A Pap looks at loose cells scraped from the surface. A biopsy looks at a small piece of tissue and gives the CIN grade. That is why treatment decisions usually rest on the biopsy, not the Pap alone.

When a Pap test reads HSIL, the biopsy confirms a high-grade change in about 96 out of 100 cases.³ So an HSIL Pap result is taken seriously and almost always leads to a closer look rather than a repeat Pap. The word “high-grade” describes how abnormal the cells look, not how far anything has spread.

How HPV Turns Normal Cells Into HSIL

High-risk HPV makes two proteins that drive infected cells to keep dividing.⁴ One destroys a protein that normally stops damaged cells from dividing.⁵ The other breaks down a second brake protein, pushing cells into dividing too early.⁶ In biopsies, that brake fades as the viral protein rises from low-grade to higher-grade lesions.⁷ So HSIL reflects an infection that has taken over cell growth, not just a passing one.

Most sexually active people get HPV at some point and clear it. HSIL develops only when a high-risk type lingers for years. Smoking and a weakened immune system make clearance harder. Having HSIL says nothing about recent sexual behavior or a partner’s faithfulness. The change from infection to HSIL unfolds over years, not weeks, and the virus can sit unnoticed without symptoms, which is why HSIL is typically found on screening rather than felt.

How Likely HSIL Is to Become Cancer

HSIL is more likely than low-grade changes to progress and less likely to go away.⁸ Left untreated over about 30 years, roughly 30% of HSIL is estimated to become invasive cancer.⁹ Over a shorter span, about 1 to 2 in every 100 women with untreated HSIL develop cervical cancer.¹⁰ For women aged 20 to 24 with CIN3, the chance of cancer within one year is about 0.5%.¹¹

The 30% figure is an estimate across many women, not a prediction for any single person. Treatment is offered because the risk is meaningful and removing the lesion is low-risk by comparison. Doctors cannot tell which lesions will advance, which is why most HSIL, especially CIN3, is treated.

High-grade lesions are most common in women in their late 20s and 30s.¹² In North America they tend to peak before age 30, slightly younger than in other regions.¹³ Actual cervical cancer is more common in older women, especially over 60.¹⁴

What Happens After an HSIL Result

The next step is usually colposcopy, a magnified look at the cervix after the doctor applies a vinegar solution that makes abnormal areas show white. The doctor then takes small tissue samples from areas that look abnormal. Colposcopy alone misses many high-grade areas; in one large clinic it found only about 56% of them.¹⁵ So biopsies, sometimes several, matter more than how the cervix looks.

The exam feels like a long Pap test and takes about 10 to 20 minutes. Biopsies cause a brief pinch or cramp. Expect light spotting or dark discharge for a few days. Results usually arrive within one to two weeks.

To prepare, schedule the visit for a time when you are not on your period, since heavy bleeding can make the cervix harder to see. Many clinics advise avoiding sex, tampons and vaginal creams for a day or two beforehand, so ask what your clinic wants. An over-the-counter pain reliever is often suggested for cramping, but check with the clinic first. If you are pregnant or might be, tell the doctor, because the biopsy approach is adjusted.

Sometimes a Pap reads HSIL while the biopsy shows something milder. That may mean the worst area was missed. Doctors may still recommend treatment or a closer recheck, so ask how yours weighed both results.

Your biopsy report may mention p16, a stain that lights up cells where HPV is actively driving growth.¹⁶ It is positive in most CIN2 biopsies, about 84%.¹⁷ When a pathologist already sees clear CIN2 or CIN3, the stain rarely changes the grade, about 1 in 84 cases.¹⁸ In women after menopause, the p16 stain helps tell HSIL from normal thinning of tissue that can look similar.¹⁹

Can HSIL Go Away on Its Own

Often, in young women. In women under 25, CIN2 shrank to a lower grade in about 75 to 88% of cases while being watched.²⁰²¹ Regression typically took 11 to 21 months.²²²³ CIN3 regressed in only about 29% of these young women.²⁴ Regression was more likely when HPV cleared and in women vaccinated against HPV.²⁵ So watching is mainly offered for CIN2 in younger women, especially those planning pregnancy. Cervical cancer is rare under 25, so the short-term risk of waiting is low, and avoiding treatment matters for later pregnancy.

Watchful waiting means repeat colposcopy and Pap or HPV tests about every six months, with treatment if the lesion persists or worsens. In one group, about 7 in 10 eventually needed surgery anyway.²⁶ The main risk of this approach is missing follow-up visits.

Treatments That Remove or Destroy HSIL

Most often, treatment is LEEP, short for loop electrosurgical excision procedure. It uses a thin heated wire loop to remove a small cone of tissue containing the abnormal area, usually under local anesthetic. Cold-knife cone uses a scalpel instead, often in an operating room. In one review of 447 cases, abnormal cells reached the edge of the removed tissue in about 31% of LEEPs and 22% of cone biopsies, a difference that may be chance.²⁷ A “positive margin” is therefore common, and it leads to closer follow-up, not automatically more surgery.

The LEEP itself takes around 10 minutes in a clinic. Cramping is common, and discharge or spotting can last a few weeks. Avoid sex, tampons and baths for about four weeks. Heavy bleeding or fever needs a call to the doctor.

The removed tissue goes to the lab, where it is examined under a microscope. That gives a more complete answer than the first small biopsy, and occasionally it reveals something more serious than the biopsy showed, so removal serves diagnosis as well as treatment. Results typically take a week or two, and your doctor will explain what they mean for follow-up.

Thermal ablation destroys abnormal tissue with heat instead of removing it.²⁸ In a clinic comparing treatments, ablation, freezing and LEEP had similar success, about 60 to 67%.²⁹ In selected visible lesions, ablation showed low recurrence and no cancer during follow-up.³⁰ A cream, imiquimod, made more than half of cervical HSIL regress in one study, but it is not standard.³¹

Treatment and Future Pregnancy

After LEEP, about 8.8% of births were preterm, compared with 5.1% without LEEP.³² But compared with women who had abnormal cells and no surgery, the difference nearly disappeared, 10.0% versus 7.2%, and that gap could be chance.³³ Part of the link comes from the disease itself, since women with cervical abnormalities may already have somewhat higher preterm risk before treatment. LEEP is also linked with more early water breaking and lower birth weight.³⁴ A cervix shorter than 3 cm in pregnancy is more common after LEEP.³⁵ So tell your obstetrician about any LEEP so they can check cervix length.

If you hope to get pregnant, ask whether watching is safe for your grade and age, and how much tissue the doctor plans to remove. Most women have healthy full-term pregnancies after LEEP.

Follow-Up and the Chance It Comes Back

HSIL is more likely to return when HPV is still present after LEEP, the follow-up Pap is abnormal, or abnormal cells reached the inner margin.³⁶ Being 35 or older raised the risk about fivefold in women with positive margins.³⁷ An abnormal Pap within the first year after treatment is a warning sign.³⁸ So keep every follow-up visit, usually with HPV testing around 6 months after treatment.

A typical schedule starts with HPV and Pap co-testing at about 6 months. Testing then repeats yearly until several results are clear, followed by a return to routine screening for at least 25 years.

A negative HPV test after treatment is reassuring, since it suggests the virus is no longer detectable in the cervix, though follow-up still continues. A positive test does not mean treatment failed, but it calls for closer attention.

Vaccination seems to help. High-grade lesions came back in 3.3% of women vaccinated around their LEEP versus 13.6% of unvaccinated women.³⁹ Ask your doctor about HPV vaccination even after treatment.

Women with HIV have more treatment failure, especially when viral load is detectable.⁴⁰ Ablation failed far more often than cone removal in women with HIV.⁴¹ Keeping HIV well controlled supports cervical treatment success.

HSIL Outside the Cervix

The anus, vulva and vagina can also develop HPV-driven HSIL. Anal HSIL is the precursor to anal cancer and develops much like cervical HSIL.⁴² In people with HIV, it often returns, 30 to 70% across treatments, mostly as new spots.⁴³ Vulvar HSIL is HPV-related and differs from another, HPV-unrelated vulvar precancer with a different risk.⁴⁴ Report itching, sores or lumps around the vulva or anus, especially if you have had cervical HSIL. Anal screening is worth asking about if you live with HIV, have a history of cervical or vulvar HSIL, or have had an organ transplant or other immune suppression.

Screening can use an anal Pap test, followed by a magnified exam of the anus called high-resolution anoscopy if the Pap is abnormal. Treatment options include office-based methods that destroy the lesion, topical medicines, or surgical removal. Because recurrence is common, monitoring continues after treatment.

Coping With the Worry of an Abnormal Result

Anxiety rises sharply after an abnormal result, and for most women it fades.⁴⁵ About 35% still had significant anxiety 12 weeks later, more often when they did not fully understand their result.⁴⁶ Ask your doctor to explain your grade, your next step and your actual risk in plain terms.

It helps to bring questions to the appointment: Is my result CIN2 or CIN3? Is watching an option for me? Which treatment do you recommend and why? When is my follow-up test?