This article was reviewed and updated on July 30, 2019.

by Jason Wasserman, MD PhD FRCPC

Quick facts:

  • Endometriosis is a non-cancerous condition that develops when the tissue normally found on the inside of the uterus starts growing in another part of the body.

  • Common locations for endometriosis are the ovaries, fallopian tubes, and colon.

  • The most common symptom of endometriosis is pain.

The normal endometrium

​The inner lining of the uterus is called the endometrium. The purpose of the endometrium is to provide support for a fertilized egg to develop and grow. The inner surface of the endometrium is lined by epithelial cells that connect together to form glands. The tissue in between the glands is called stroma and its role is to provide support for the glands.

What is endometriosis?

Endometriosis is a non-cancerous condition that occurs when glands and stroma from the endometrium are found outside in any tissue outside of the endometrium.


Common locations for endometriosis are the ovaries, fallopian tubes, and colon (large bowel), however, endometriosis can occur anywhere in the body.

Many women with endometriosis experience pain and the pain may be worst at the same time as their normal menstrual period.

Over time, endometriosis can cause large blood filled cysts to develop. These cysts can become very large and may eventually need to be removed.

Although endometriosis is considered a non-cancerous condition, it is associated with an increased risk of cancer. In particular, when endometriosis involves the ovary, it is believed to provide the 'seed' for the development of clear cell carcinoma and endometrioid carcinoma.


Why is this important? While many women have endometriosis, very few will develop either of these cancers and so the risk is actually very low.

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