Adenocarcinoma in situ (AIS)

By Jason Wasserman MD PhD FRCPC
March 22, 2023

What is adenocarcinoma in situ?

Adenocarcinoma in situ (AIS) is a non-invasive type of cancer. It is called non-invasive because the cancer cells have not spread into surrounding tissues. If left untreated, it can turn into invasive adenocarcinoma.

adenocarcinoma in situ
Adenocarcinoma in situ. In this picture half of the gland (right side) has been replaced by adenocarcinoma in situ.

Is adenocarcinoma in situ a benign or malignant disease?

AIS is considered a malignant (cancerous) disease. However, it is also non-invasive which means that cancer cells have not yet spread into surrounding tissues. As long as the disease remains non-invasive, the cancer cells can also not spread to other parts of the body.

What causes adenocarcinoma in situ?

The cause of AIS depends on the location of the tumour. In the lung, AIS is strongly associated with long-term exposure to tobacco smoke. In the cervix, most cases of AIS are caused by infection with human papillomavirus (HPV).

Where is adenocarcinoma in situ found in the body?

The two most common locations for AIS are the lung and the cervix. In the past, the diagnosis AIS was also applied to tumours arising in the stomach, esophagus, and colon. However, other terms such as intramucosal carcinoma and high grade dysplasia are now preferred in those locations.

Learn more about your pathology report for adenocarcinoma in situ of the lung or cervix.

Can the cancer cells in adenocarcinoma in situ spread to other parts of the body?

No. The cancer cells in AIS cannot spread to other parts of the body. Cancer cells use blood vessels and lymphatic vessels to spread to other parts of the body. However, like all non-invasive types of cancer, the cancer cells in AIS do not have access to blood vessels and lymphatic vessels. As a result, the cancer cells cannot spread to other parts of the body.

What is the difference between adenocarcinoma in situ and adenocarcinoma?

AIS is a non-invasive type of cancer while adenocarcinoma is an invasive type of cancer. This is an important difference because, unlike adenocarcinoma, the cancer cells in AIS are unable to spread to other parts of the body.

What stage is adenocarcinoma in situ?

Depending on the part of the body involved, AIS is staged as pT0 or pTis. Both stages indicate that AIS is a non-invasive type of cancer.

How is adenocarcinoma in situ diagnosed?

The diagnosis of AIS can be made after tissue is examined under the microscope by a pathologist.

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