Endometriosis and Ovarian Cancer: Is there a connection?

Ovarian Cancer

This article was written for The Endometriosis Network Canada by Ovarian Cancer Canada, the only national organization dedicated to overcoming ovarian cancer, providing leadership through: support for women and their families living with the disease; raising awareness; providing education for the general public and health care providers; and funding research for early detection, improved treatment and ultimately, a cure. www.ovariancanada.org/1-877-413-7970

Ovarian cancer is often overlooked and underdiagnosed, yet it is the most fatal women’s cancer. Each year in Canada, 2,600 women are diagnosed and 1,750 women die. Sadly, the five-year survival rate is about 30% for women diagnosed in advanced stages of the disease. Often thought to have a screening test or vaccine, this disease is not always at the top of mind for women. Quite often the PAP test and the HPV vaccine are thought to be for ovarian cancer but they are for cervical cancer only. Ovarian cancer can be difficult to detect as the primary symptoms of ovarian cancer are very common and vague: bloating, difficulty eating or feeling full quickly, abdominal pain and any change in urinary habits.

Research into ovarian cancer has exploded in recent years and everyday there is more understanding about this disease. One of the key discoveries is that ovarian cancer is not just one disease, it is many diseases and is far more complex than originally thought. Epithelial ovarian cancer is the most common type and this type is broken down into five different subtypes: serous; endometrioid; clear cell; mucinous; and undifferentiated. Each of these subtypes is different with different origins and pathology. For instance, the most common type of ovarian cancer is high grade serous epithelial cancer. It is now thought that the origin of this ovarian cancer is the fallopian tubes. As a result of this finding, new guidelines by the B.C. Cancer Agency state that if a woman is having gynecologic surgery that is unrelated to cancer i.e. a tubal ligation or removal of her uterus, she should have her fallopian tubes removed as a preventive measure for ovarian cancer.

Recent research has also found a relationship between endometriosis and ovarian cancer, specifically clear cell and endometrioid epithelial ovarian cancer, which will be discussed below.

The priority risk factors for ovarian cancer include: family history of ovarian, breast, uterine and colon cancers; age – most common in women over 50; ethnicity – women of Ashkenazi Jewish ancestry are at higher risk for ovarian cancer because of a higher pre-disposition for the BRCA genetic mutations. Other possible at risk groups of women include French Canadian and Icelandic women. A woman with a BRCA genetic mutation is at higher risk for both ovarian and breast cancer.

Factors that can reduce a woman’s risk for ovarian cancer include: use of oral contraceptives; multiple children; removal of ovaries and fallopian tubes. Hormonal treatment of endometriosis can help reduce symptoms of endometriosis. It may also turn out that it could help reduce the risk of clear cell and endometrioid ovarian cancer.

Can endometriosis increase the risk for ovarian cancer?

It can, however it should be stressed that the increased risk is very small. Endometriosis is associated with only two subtypes of ovarian cancer – endometrioid and clear cell epithelial ovarian cancers – which are not as common as other subtypes. Endometriosis can increase the risk for these cancers three-fold. However, given that the lifetime risk for ovarian cancer in general is 1.4%, the increased risk for women with endometriosis is only slightly higher at 1.95%.

Can untreated endometriosis/endometriomas turn into ovarian cancer?

Treated and untreated endometriosis can turn into ovarian cancer, however, it should be stressed that not all women with endometriosis will develop ovarian cancer. Researchers do not know why some women with endometriosis develop cancer and some do not. It is also not yet understood why some develop clear cell ovarian cancer and some develop endometrioid ovarian cancer. Researchers have noted that there are some shared genetic mutations between both of these types of cancer and some unique mutations. There also seems to be a precursor lesion to endometrioid and clear cell cancers (termed atypical endometriosis) that can also harbour some of the mutations.

Although endometriosis is strongly associated with these two subtypes of ovarian cancer, having endometriosis does not mean you will develop ovarian cancer and the overall risk is low.

As stated above, hormonal treatment of endometriosis can help reduce symptoms of endometriosis. There is a possibility that it could also help reduce the risk of clear cell and endometrioid ovarian cancer. More research is needed to fully understand this relationship between endometriosis and ovarian cancer.

What about the CA-125? Should endometrial patients use this test to screen for ovarian cancer?

No. The CA125 is not a screening test for the general population for ovarian cancer as it can have false positive and false negative results. It is especially not a helpful tool for women with endometriosis as benign endometriosis can raise CA125 levels.

What about BRCA 1 and 2 and genetic testing?

BRCA1 and 2 genetic mutations are associated almost exclusively with high grade serous epithelial cancer. Therefore, there is no need to test for this mutation in women with endometriosis or endometrial associated ovarian cancers (clear cell and endometrioid) unless there is a family history of breast and/or ovarian cancer.

Endometrial associated ovarian cancers are, however, associated with a different genetic mutation called Hereditary Non-Polyposis Colorectal Cancer (HNPCC) or Lynch Syndrome. Lynch Syndrome is associated with increased lifetime risk of colorectal, endometrial and ovarian cancers. If there is a strong family history of these cancers, speak to your doctor about a referral to a genetics counsellor.

Most ovarian cancer actually starts in the fallopian tubes. Is this the case for the types of ovarian cancer associated with endometriosis?

No. The type of ovarian cancer that often starts in the fallopian tubes is high grade serous ovarian cancer. This is not the case for clear cell or endometrioid ovarian cancer.

What should a woman with endometriosis do?

It is important for a woman to know her body, know the symptoms of ovarian cancer and what her body feels like in its “normal” state. That may include ongoing endometriosis symptoms. If something changes and a new symptom develops from the list above or an existing one intensifies, is frequent and persists for 3 weeks or longer, a woman should see her doctor to determine the cause. Chances are it is not ovarian cancer, but it is important to seek medical attention. Three tests that can be used in conjunction with each other to detect ovarian cancer are a pelvic exam, transvaginal ultrasound and CA125 blood test. Given the presence of endometriosis, the physician may not want to use the CA125 blood test because of the risk of a false positive result.

It is also important for a woman to be aware of her family history including both the mother’s and father’s side of the family. If a woman has a strong history of ovarian, uterine, colon or breast cancers, she should talk to her doctor and consider a referral to a genetics counsellor.

If you would like further information or a presentation about ovarian cancer to a community group or office, please contact Ovarian Cancer Canada.