Cervical Cancer Series 05 What Is CIN? Understanding Cervical Intraepithelial Neoplasia
After an abnormal Pap test or HPV test, some people undergo a biopsy and see terms such as “CIN1,” “CIN2,” or “CIN3” in their pathology report.
Because these unfamiliar terms are followed by numbers, it is easy to assume that they refer to stages of cervical cancer.
“Does CIN3 mean stage 3 cervical cancer?”
“If it is called a precancerous lesion, does that mean cancer has already started?”
“Will it turn into cancer if I am not treated immediately?”
However, CIN1, CIN2, and CIN3 are not stages of cervical cancer. CIN refers to abnormal changes in the cells lining the surface of the cervix. These changes have not invaded the surrounding tissue and are not invasive cervical cancer.
The likelihood that CIN will regress on its own or progress toward cancer differs by grade. Understanding what CIN means and following a management plan based on your individual test results are therefore important.
A Pap Test Result and a CIN Diagnosis Are Not the Same
A Pap test is a screening test that examines cells collected from the cervix under a microscope. Its purpose is to detect abnormal cervical cells and identify people who may need further evaluation.
Pap test results may include terms such as ASC-US, LSIL, and HSIL.
However, finding abnormal cells on a Pap test does not automatically establish a CIN grade. Depending on the Pap test and HPV test results, previous screening history, and individual risk, repeat testing or colposcopy may be recommended.
Colposcopy uses a magnifying instrument to examine the cervix more closely. If an area appears abnormal, a small tissue sample may be removed for a biopsy.
CIN1, CIN2, and CIN3 are histologic diagnoses generally made after a pathologist examines this tissue under a microscope.
LSIL on a Pap test may be associated with CIN1 on biopsy, while HSIL may be associated with CIN2 or CIN3. However, the terms do not always match because a Pap test examines collected cells as a screening test, whereas a biopsy evaluates changes within cervical tissue.
CIN Is an Abnormal Change in the Cervical Epithelium
CIN stands for cervical intraepithelial neoplasia.
The surface of the cervix is covered by several layers of epithelial cells. HPV infection can cause changes in these cells. In particular, persistent infection with a high-risk HPV type increases the likelihood of developing a high-grade lesion.
In CIN, the abnormal cells remain within the epithelium covering the cervix. They have not crossed the boundary of the epithelium, invaded deeper tissue, or spread elsewhere.
In invasive cervical cancer, by contrast, abnormal cells have crossed this boundary and invaded the surrounding tissue.
CIN is therefore not the same diagnosis as cervical cancer. However, some CIN lesions can eventually progress to cervical cancer, which is why they are classified as precancerous lesions.
The term “precancerous” does not mean that cancer is already present. It means that the cells have changed in a way that could progress to cancer in some cases if not appropriately managed.
CIN1, CIN2, and CIN3 Are Not Cancer Stages
The numbers following CIN have a completely different meaning from stage 1, stage 2, or stage 3 cervical cancer.
Cancer staging describes how far cancer has spread into nearby tissues or other parts of the body. CIN grading, however, describes how much of the thickness of the cervical epithelium contains abnormal cells.
CIN1 is a mild change in which abnormal cells are found mainly in approximately the lower one-third of the epithelium.
CIN2 is a moderate change in which abnormal cells extend through approximately two-thirds of the epithelial thickness.
CIN3 is a severe change in which abnormal cells involve more than two-thirds or nearly the full thickness of the epithelium.
In current pathology terminology, CIN1 may also be classified as a low-grade squamous intraepithelial lesion, or LSIL, while CIN2 and CIN3 may be classified as high-grade squamous intraepithelial lesions, or HSIL.
A higher number generally indicates that abnormal cells involve a larger portion of the epithelium and carry a greater risk of progressing to cancer. It does not indicate how far cancer has spread.
CIN1 Usually Does Not Require Immediate Treatment
CIN1 often reflects a temporary cellular response to HPV infection.
When the immune system brings the HPV infection under control, the abnormal cell changes may also disappear. Spontaneous regression is particularly common in younger people.
For this reason, finding CIN1 does not usually mean that the abnormal tissue must be removed immediately. Instead, follow-up testing is generally used to determine whether the changes disappear, persist, or progress to a higher grade.
Treatment may be considered if CIN1 continues to be detected over a prolonged period. Even then, the decision takes into account previous test results, whether HPV infection persists, the condition of the lesion, and the patient’s preferences.
Observation does not mean ignoring the lesion. It is an active management approach that avoids unnecessary procedures when spontaneous regression is likely while using appropriate follow-up tests to monitor the condition safely.
CIN2 Management Depends on Individual Circumstances
CIN2 involves more extensive cellular changes and carries a higher risk of progression than CIN1. However, some CIN2 lesions can still regress without treatment.
Studies have found that approximately half of CIN2 lesions managed with observation regress spontaneously, with higher regression rates among people younger than 30. Other lesions may persist or progress to CIN3 or, less commonly, invasive cervical cancer.
These figures represent outcomes across study populations. They cannot predict whether a particular person’s lesion will regress or progress.
CIN2 is therefore not managed in exactly the same way for everyone. Treatment is generally recommended for CIN2, but observation for a limited period may be considered for selected patients who are particularly concerned about the possible effects of treatment on a future pregnancy.
Observation may be considered only when the squamocolumnar junction and the upper limit of the lesion are fully visible during colposcopy, endocervical sampling does not show CIN2 or a more severe lesion, and the patient can complete follow-up examinations as scheduled.
If observation is selected, colposcopy and cervical testing must be performed at intervals determined by the clinician. Treatment is recommended if CIN2 persists for a prolonged period or progresses to CIN3.
The choice is therefore not simply between always treating CIN2 and always waiting. Management should account for the lesion’s risk, the patient’s age, previous test results, pregnancy plans, and ability to complete regular follow-up.
CIN3 Generally Requires Treatment
CIN3 is a high-grade lesion in which severe cellular changes involve a large portion of the cervical epithelium.
CIN3 does not mean stage 3 cervical cancer. If the abnormal cells have not crossed the boundary of the epithelium and invaded the surrounding tissue, the condition is not invasive cervical cancer.
However, untreated CIN3 has a greater risk of progressing to cancer than CIN1 or CIN2. Current testing cannot reliably predict which CIN3 lesions will remain confined to the epithelium and which will eventually become invasive cancer.
For this reason, treatment rather than observation is generally recommended for CIN3, except in special circumstances such as pregnancy.
It is important not to postpone recommended treatment simply because CIN3 is not yet cancer. Treating CIN3 at the appropriate time can prevent it from progressing to invasive cervical cancer.
Treatment Aims to Remove Abnormal Tissue
The purpose of CIN treatment is to remove or destroy abnormal tissue that has a meaningful risk of progressing to cancer.
Common treatment methods include the loop electrosurgical excision procedure, known as LEEP or LLETZ, and cone biopsy.
LEEP uses a thin wire loop carrying an electrical current to remove abnormal tissue from the cervix.
A cone biopsy removes a cone-shaped section of the cervix and cervical canal containing the abnormal cells. It may be performed depending on the location and extent of the lesion or when invasive cancer is suspected.
In some situations, abnormal tissue may be destroyed using treatments such as laser therapy or cryotherapy. For high-grade lesions such as CIN2 and CIN3, however, excisional treatment is often preferred because the removed tissue can be examined by a pathologist.
The treatment method is not determined by the CIN grade alone. Clinicians also consider the lesion’s size and location, whether it extends into the cervical canal, previous treatment history, age, and future pregnancy plans.
Most people can still become pregnant after LEEP or cone biopsy. However, removing a large or deep amount of cervical tissue or undergoing repeated procedures may increase the risk of pregnancy-related complications such as preterm birth.
If you plan to become pregnant in the future, tell your clinician before treatment and discuss both the lesion’s risk and the amount of tissue that may need to be removed.
Follow-Up Must Continue After Treatment
Removing abnormal tissue does not eliminate all future risk.
High-risk HPV infection may remain, or new cellular changes may develop. If abnormal cells are found at the margins of the removed tissue, further testing or treatment may also be necessary.
After treatment, follow your clinician’s schedule for HPV testing or cotesting with both an HPV test and a Pap test.
People treated for a high-grade lesion do not immediately return to a routine cervical cancer screening schedule, even when their initial follow-up results are normal. After the initial post-treatment surveillance period, U.S. ASCCP guidelines recommend HPV-based surveillance at three-year intervals for at least 25 years.
This follow-up may continue beyond the age when routine cervical cancer screening would otherwise end. The exact timing and type of testing may vary depending on treatment results, age, overall health, and previous screening history.
Do not discontinue follow-up on your own simply because a test result is normal.
What Should You Confirm After a CIN Diagnosis?
If you have been diagnosed with CIN, first confirm whether the pathology result is CIN1, CIN2, or CIN3.
You should then review the following questions with your clinician:
Was a high-risk HPV type detected?
Were previous Pap tests or HPV tests also abnormal?
Were the squamocolumnar junction and the upper limit of the lesion fully visible during colposcopy?
Did endocervical sampling show CIN2 or a more severe lesion?
Is observation or treatment recommended?
If treatment is needed, which procedure is recommended?
Could the treatment affect a future pregnancy?
When should the next test be performed, and which test will be used?
A CIN grade alone is not enough to decide on treatment without medical guidance. Even among people with CIN2, management may differ according to age, screening history, lesion characteristics, pregnancy plans, and the ability to complete regular follow-up.
Key Takeaways
CIN is not cervical cancer. It is an abnormal change in the epithelial cells lining the surface of the cervix.
CIN1, CIN2, and CIN3 are grades describing how much of the cervical epithelium contains abnormal cells. They are not stages of cervical cancer.
CIN1 often regresses spontaneously and is generally monitored rather than treated immediately.
CIN2 requires consideration of both its potential to regress and its risk of progression. Treatment is generally recommended, but selected patients who meet specific criteria and can attend regular follow-up may choose observation after discussing the options with their clinician.
CIN3 is not invasive cervical cancer, but it carries a higher risk of progressing to cancer and generally requires treatment.
Even after abnormal tissue has been removed, high-risk HPV infection may remain or new cellular changes may develop. Long-term follow-up is therefore necessary.
If you have been diagnosed with CIN, do not assume that the number means cancer or postpone recommended treatment and follow-up on your own. Review the biopsy findings, HPV test results, previous screening history, and future pregnancy plans with your clinician to determine the management approach that is most appropriate for you.
References
National Cancer Institute. HPV and Pap Test Results: Next Steps After an Abnormal Test
Perkins RB, Guido RS, Castle PE, et al. 2019 ASCCP Risk-Based Management Consensus Guidelines for Abnormal Cervical Cancer Screening Tests and Cancer Precursors. Journal of Lower Genital Tract Disease. 2020;24(2):102–131.
Tainio K, Athanasiou A, Tikkinen KAO, et al. Clinical Course of Untreated Cervical Intraepithelial Neoplasia Grade 2 Under Active Surveillance: Systematic Review and Meta-Analysis. BMJ. 2018;360:k499.
National Cancer Institute. Cervical Cancer Screening (PDQ®)—Health Professional Version
World Health Organization. Treatment of Cervical Intraepithelial Neoplasia 2–3 and Adenocarcinoma in Situ. WHO Guidelines. 2014.
International Agency for Research on Cancer. Colposcopy and Treatment of Cervical Precancer. IARC Technical Publication No. 45. 2017.
Kyrgiou M, Athanasiou A, Paraskevaidi M, et al. Adverse Obstetric Outcomes After Local Treatment for Cervical Preinvasive and Early Invasive Disease According to Cone Depth: Systematic Review and Meta-Analysis. BMJ. 2016;354:i3633.
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