Adenocarcinoma in situ of the cervix

by Jason Wasserman MD PhD FRCPC
August 8, 2025

Adenocarcinoma in situ (AIS) of the cervix is a precancerous condition in which abnormal glandular cells grow on the surface of the cervix. These abnormal cells look like those seen in adenocarcinoma, a type of cervical cancer, but in AIS, the abnormal cells are confined to the surface layer and have not invaded deeper tissues. Because AIS can progress to invasive cancer over time, it is considered a serious but treatable condition.

There are two main types of AIS. Most cases are linked to high-risk human papillomavirus (HPV) infection and are called HPV-associated AIS. A smaller number of cases are not related to HPV infection and are known as HPV-independent AIS. These two types differ in their development, microscopic appearance, detection methods, and treatment options.

Early diagnosis and treatment of AIS can prevent the development of invasive cervical cancer. In most cases, AIS is detected through routine cervical screening (Pap tests and HPV testing), although some cases—especially HPV-independent AIS—may be harder to identify and are only found during procedures performed for other reasons.

What are the symptoms of adenocarcinoma in situ?

Many people with adenocarcinoma in situ of the cervix do not experience symptoms, especially in early stages. Usually, the condition is found during routine cervical cancer screenings like a Pap test, an HPV test, or both. This is particularly true for HPV-associated AIS, which often develops in areas that are more accessible during screening.

When symptoms do occur, they may include abnormal vaginal bleeding, such as bleeding between periods or after intercourse, or an unusual watery vaginal discharge. These symptoms are not specific to AIS and can also be caused by other, less serious conditions. HPV-independent AIS, including gastric-type AIS, is more likely to cause noticeable symptoms, such as persistent watery discharge, and is more difficult to detect on a Pap test.

Because AIS can develop without symptoms, regular cervical screening is the best way to find this condition early, before it progresses to invasive cancer.

What causes adenocarcinoma in situ?

Adenocarcinoma in situ of the cervix can develop through two different pathways. The most common type results from persistent infection with high-risk types of human papillomavirus (HPV), known as HPV-associated AIS. A less common form, called HPV-independent AIS, is not linked to HPV infection. Instead, it exhibits features similar to the cells found in the stomach, a pattern known as gastric-type differentiation. These two types of AIS appear different under the microscope and exhibit different behaviors over time.

HPV-associated adenocarcinoma in situ

HPV-associated AIS results from long-term infection with high-risk HPV types, primarily HPV16, HPV18, and HPV45. These viruses can cause abnormal changes in the glandular cells lining the cervix. Most individuals infected with HPV clear the virus naturally, but in some cases, the virus remains in the body and can lead to precancerous conditions like AIS.

This type of AIS is most often diagnosed in people in their 30s or 40s, and it is more likely to be missed during routine cervical screening because it develops high in the endocervical canal. HPV-associated AIS is almost always positive for HPV DNA or RNA when tested and typically shows changes in the affected cells that make the diagnosis clear under the microscope.

HPV-independent adenocarcinoma in situ

HPV-independent AIS is a much rarer condition and is not related to HPV infection. It tends to occur in people over the age of 50 and often presents without symptoms or is found incidentally during surgery for another condition. This type of AIS shows gastric-type differentiation, meaning the abnormal cells resemble the mucin-producing cells that line the stomach. These cells produce a pale or yellowish substance called mucin, which helps distinguish this form of AIS from other types.

The cause of HPV-independent AIS is unknown, and it may follow a different pathway of disease development in the cervix. Because this type is not detected by HPV testing, it might be harder to diagnose with routine screening methods.

Is adenocarcinoma in situ the same as cervical cancer?

No. AIS is not cancer, but it is a precancerous condition that can develop into invasive adenocarcinoma if left untreated. AIS is confined to the surface epithelium and does not invade deeper tissues. With early treatment, AIS can often be completely removed and cured.

How is the diagnosis of adenocarcinoma in situ made?

Adenocarcinoma in situ of the cervix is diagnosed by examining a tissue sample from the cervix under a microscope. This process is performed by a pathologist, a doctor who specializes in studying diseases in tissues. The tissue may be collected using different procedures, depending on the patient’s symptoms, screening results, and risk factors.

• Pap test (Pap smear): A Pap test is a screening procedure used to detect abnormal cells on the surface of the cervix. It involves gently brushing or scraping cells from the cervix. These cells are then placed on a slide and examined under a microscope. Although AIS can be challenging to diagnose through a Pap test alone, it may identify abnormal glandular cells that indicate the need for further testing. Results may be reported as atypical glandular cells leading to follow-up procedures.
• Colposcopic biopsy: If the Pap test or HPV test results are abnormal, the next step is usually a colposcopy. During this procedure, a doctor uses a colposcope (a special magnifying instrument) to carefully examine the cervix. A small tissue sample is taken from any suspicious areas. This sample is then sent to the pathology lab for microscopic analysis. Colposcopic biopsy provides a more targeted evaluation but may not detect deeper or more widespread disease if AIS is located higher in the endocervical canal.
• Loop electrosurgical excision procedure (LEEP) or cone biopsy: These procedures remove a larger portion of tissue from the cervix and are often used to confirm a diagnosis of AIS or to completely remove the abnormal area. LEEP uses a thin wire loop heated by electric current to cut away a layer of cervical tissue. A cone biopsy, also called conization, removes a cone-shaped section of the cervix, which includes the transformation zone where most cervical abnormalities develop. These procedures provide a larger sample for the pathologist to examine, helping determine how much of the cervix is affected and whether any cancer is present.

What does adenocarcinoma in situ look like under the microscope?

When examined under the microscope, adenocarcinoma in situ (AIS) shows abnormal glandular cells that are still confined to the surface lining of the cervix. These cells have not yet invaded deeper layers of tissue, which is why AIS is considered a precancerous condition.

In HPV-associated AIS, the abnormal cells are tall and column-shaped and may produce little or no mucin (a jelly-like substance found in normal cervical cells). These cells often appear crowded, with dark, elongated nuclei that form layers. The nuclei frequently show signs of active growth, including visible mitotic figures (cells dividing) and nuclear fragmentation, called karyorrhexis. The abnormal cells usually follow the shape of the normal glands but can also form complex patterns with small cribriform (sieve-like) spaces or papillary (finger-like) structures.

In HPV-independent AIS, especially gastric-type AIS, the cells are often cuboidal or columnar, with clear or foamy cytoplasm filled with mucin. The nuclei are frequently enlarged and irregular but usually less active than in HPV-associated AIS. The abnormal cells stay within the normal gland structures, although they can sometimes form slightly more complex arrangements. These cells resemble those found in the stomach lining, a feature called gastric-type differentiation. Sometimes, intestinal features such as goblet cells (mucus-secreting cells) can also be seen.

Both types of AIS can be subtle under the microscope, particularly in early or superficial lesions. Precise diagnosis depends on carefully evaluating cell appearance and growth patterns.

What other tests may be performed to confirm the diagnosis?

In some cases, additional tests are performed to support the diagnosis of adenocarcinoma in situ (AIS) and to differentiate it from other conditions. These tests help confirm whether the abnormal cells are associated with HPV and if the lesion is pre-cancerous.

Immunohistochemistry (IHC)

IHC is a specialized test that uses antibodies to detect specific proteins in tissue. For HPV-associated AIS, one of the key markers is p16, which is strongly and diffusely positive in nearly all cases. This staining pattern, called “block-type,” confirms that the abnormal cells are likely driven by high-risk HPV infection. Another useful marker is Ki-67, which indicates how actively the cells are dividing. In AIS, the Ki-67 level is usually high, reflecting rapid cell growth.

In HPV-independent AIS, p16 is typically negative or exhibits only patchy staining. Conversely, other markers such as MUC6, CK7, and HIK1083 may test positive, aiding pathologists in identifying gastric-type differentiation. Hormone receptors like estrogen receptor (ER) and progesterone receptor (PR) are usually negative or only weakly positive, further supporting the diagnosis. In some cases, abnormal expression of the protein p53 suggests a more aggressive or advanced lesion.

In situ hybridization (ISH)

ISH is a test that detects HPV genetic material directly in cells. For HPV-associated AIS, ISH can confirm the presence of high-risk HPV, especially types 16 and 18. This test is useful when the diagnosis is uncertain or when p16 staining is unclear. ISH can identify either DNA or RNA from the virus, with RNA-based tests generally offering more specific results.

ISH is usually not useful for diagnosing HPV-independent AIS, as these lesions are not caused by HPV and will not produce positive HPV signals. A negative HPV test result supports the diagnosis of HPV-independent AIS when other characteristics are consistent.

Genotyping

HPV genotyping is a test that determines the specific type of HPV in the tissue. This test is mainly used in HPV-associated AIS to confirm infection with high-risk types such as HPV16, HPV18, or HPV45. Identifying the specific HPV type can offer beneficial information for follow-up and risk evaluation. Genotyping is not useful for HPV-independent AIS, as these tumors are not connected to HPV infection.

What is a margin?

A margin is the edge or border of the tissue that was removed during surgery. In the case of adenocarcinoma in situ (AIS) of the cervix, margins are important because they tell your doctor whether all of the abnormal tissue was removed. After surgery, your pathologist examines the margins under a microscope to look for any AIS cells right at the cut edge of the tissue.

If AIS cells are seen at the margin, this is called a positive margin. A positive margin means that some abnormal cells may still be present in your body at that site, which increases the risk that the disease could return in the same location. If no AIS cells are seen at the margin, this is called a negative margin, which means the abnormal tissue was likely removed completely.

The type and number of margins described in your pathology report depend on the kind of surgery performed. Procedures that remove the entire lesion, such as a cone biopsy or hysterectomy, will have margins that can be assessed. Smaller procedures, like Pap smears or tiny biopsies, do not remove the whole lesion and therefore do not have margins.

For cervical surgery, common margins include:

• Endocervical margin – This is the inner edge of the cervix where it meets the lower part of the uterus.

• Ectocervical margin – This is the outer edge of the cervix closest to the vagina.

• Stromal margin – This is the deeper tissue within the wall of the cervix.

Knowing whether your margins are positive or negative helps guide the next steps in your care. A positive margin may lead your doctor to recommend additional surgery or closer follow-up, while a negative margin is reassuring and often means no further immediate treatment is needed.

How is adenocarcinoma in situ treated?

Treatment depends on the size and type of AIS, your age, and whether you want to preserve fertility. Treatment options may include:

• Cone biopsy or loop excision to eliminate the abnormal area.
• Hysterectomy (removal of the uterus and cervix), especially if you have HPV-independent AIS or do not plan future pregnancies.
• Close follow-up with Pap smears and HPV testing if a fertility-preserving approach is chosen.

Complete excision with clear margins (no abnormal cells at the edges) is essential to reduce the risk of recurrence.

What is the prognosis for adenocarcinoma in situ?

With proper treatment, the outlook for AIS is excellent. Most individuals are cured if the abnormal cells are entirely removed.

However, follow-up is important because:

• HPV-associated AIS can recur if any abnormal tissue remains, especially if HPV infection persists.
• HPV-independent AIS may behave differently, and its long-term outcomes are less well understood. Because of this, more aggressive treatments like hysterectomy are often recommended.

Questions to ask your doctor

• Is my AIS HPV-associated or HPV-independent?
• Do I need a cone biopsy or additional testing?
• Were the abnormal cells completely removed?
• What are my treatment options, and how will they affect fertility?
• How often do I need follow-up Pap smears or HPV testing?