Adenocarcinoma in situ (AIS)
This article was last reviewed and updated on October 31, 2018
by Emily Goebel, MD FRCPC
Adenocarcinoma in situ (AIS) is a non-invasive type of cervical cancer.
Most cases are caused by a virus called human papillomavirus (HPV).
The normal cervix
The cervix is part of the female genital tract. It is found at the bottom of the uterus where it forms an opening and a canal into the endometrial cavity of the uterus.
The outer surface of the cervix is lined by two types of cells that form a barrier called the epithelium. The first part of the cervix (the part closer to the vagina) is lined by squamous cells. The second part of the cervix is called the endocervical canal and it is lined by rectangular shaped cells which connect together to make small structures called glands.
The tissue below the epithelium is called the stroma and is made up of connective tissue and blood vessels.
What is endocervical adenocarcinoma in situ (AIS)?
Endocervical adenocarcinoma in situ (AIS) is a type of non-invasive cervical cancer. The disease starts in the cervix from the glands in the endocervical canal.
AIS is called non-invasive because cancer cells are seen only in the epithelium. No cancer cells are found in the stroma below the epithelium. AIS is considered a pre-cancerous disease because over time it can turn into an invasive cancer called endocervical adenocarcinoma.
Endocervical adenocarcinoma develops when the cancer cells move from the epithelium into the stroma. The movement of cancer cells into the stroma is called invasion.
Most cases of AIS and endocervical adenocarcinoma in the cervix are a result of the normal endocervical cells in the cervix becoming infected with a high risk type of virus called human papillomavirus (HPV).
The diagnosis of AIS is usually made after a small sample of tissue is removed from the cervix in a test called a pap smear. The diagnosis can also be made after a larger sample of tissue is removed in a biopsy or resection.
A margin is any tissue that has to be cut by the surgeon in order to remove the tumour from your body. Pap smears do not have margins.
If you underwent a surgical procedure to remove the entire tumour from your body, your pathologist will examine the margin closely to make sure there are no cancer cells at the cut edge of the tissue.
The number and type of margins will depend on the type of procedure performed to remove the tumour from your body. Typical margins include:
Endocervical margin - This is where the cervix meets the inside of the uterus.
Ectocervical margin - This is the bottom of the cervix, closest to the vagina.
Stromal margin - This is the tissue inside the wall of the cervix.
A margin is considered positive when AIS is seen at the edge of the cut tissue.
Why is this important? Finding cancer cells at the margin increases the risk that the tumour will grow back in that location.
Cells infected with high risk types of human papillomavirus (HPV) produce large amounts of a protein called p16. Your pathologist may perform a test called immunohistochemistry to look for p16 inside the abnormal cells. This will confirm the diagnosis of AIS and rule out other conditions that can look like AIS under the microscope.
Why is this important? Almost all cases of AIS are positive or reactive for p16 which means your pathologist saw the p16 protein in the cancer cells.