The Connection Between Endometriosis and Ovarian Cancer

Posted 4 years ago by Andreas Obermair

Endometriosis Australia estimates over 800,000 Australian women suffer from endometriosis. Studies show that there can be a significant delay of around 7 years in the diagnosis of endometriosis.

There is currently no definitive cure for endometriosis, however there are treatments available that aim to address the symptoms and can improve quality of life.

The Connection Between Diseases

Endometriosis and cancer are two separate diseases and unfortunately, the relationship between the two is not fully understood. Studies report that women with endometriosis have an increased risk of ovarian cancer. Both depend on estrogen for their growth and both seem to be affected by inflammation. In addition, women being treated for endometriosis may also be more likely to experience infertility and either infertility or medication to treat infertility may increase the risk of ovarian cancer. However, we need to be careful not to overstate those risks, because links between the two diseases don't prove that one causes the other. Theoretically, it can also be that risk factors (e.g., oestrogen) are risk factors for both diseases independently.

The lifetime risk of ovarian cancer of women in Australia is 1.3%. Numbers of patients diagnosed with ovarian cancer are increasing with Cancer Australia reporting over 1500 cases and 1068 deaths per year. Endometriosis increases the risk of endometrioid and clear cell epithelial ovarian cancers, which are uncommon, but does not increase the risk of serous types of ovarian cancer. Endometrioid and clear cell cancers account for approximately 15% of ovarian cancers (200 of 1500 ovarian cancer patients) per year.

Ovarian Cancer Survival Rates in Women with Endometriosis

In a Dutch study of 32,419 patients with ovarian cancer, 1979 (6.1%) had endometriosis. In this study, researchers assessed the survival rate in women with ovarian cancer with or without endometriosis. Of those women with both endometriosis and ovarian cancer just over 80% of women received their diagnoses for each of the diseases within 12 months of each other.

Interestingly, women with both ovarian cancer and endometriosis had longer overall survival than women with ovarian cancer without endometriosis, even after taking into account factors such as age, cancer stage and treatment received. The average survival for those with ovarian cancer and endometriosis was 12 years, compared to 2 years for those with ovarian cancer without endometriosis.

The reason for this survival benefit is unclear; however the researchers provide a couple of potential reasons. Firstly, women with endometriosis may be more aware of physical symptoms or may also have more regular gynaecologic consultations, both resulting in the cancer being detected earlier. The researchers also found that the immune system in patients with endometriosis seems to be more active than those without, because the growth of endometriosis leads to an inflammatory response. The contraceptive pill has also been found to decrease the risk of ovarian cancer, which is a hormonal treatment commonly offered to patients with endometriosis to help reduce their symptoms.

In summary, endometriosis only increases the risk of clear-cell and endometrioid cell types of ovarian cancer. The majority of ovarian cancers are not related to endometriosis. The majority of endometriosis sufferers will never develop ovarian cancer.

The tools that we have available now are not precise enough to predict who of the many endometriosis sufferers are at a high risk of developing ovarian cancer also. I therefore, do not advocate for all women diagnosed with endometriosis to proactively reduce their risk of ovarian cancer. If surgical removal of tubes, ovaries +/- uterus is requested to protect from gynaecological cancer, it should be timed after menopause.

Further studies with molecular samples of women diagnosed with endometriosis are required to examine the association of risk and survival further.

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