Endometriosis and Cancer: What Does The Research Show?

It is not uncommon for people with endometriosis to be concerned about their risk of developing cancer in the future. Cancer and endometriosis can sometimes occur together. According to our 3rd Endometriosis In America survey, 6 percent of survey respondents have also been diagnosed with cancer, including 2 percent who have been diagnosed with cervical cancer.¹

Researchers have been exploring the connection between endometriosis and cancer for decades and have completed a variety of different studies. However, there is still no scientific consensus on the relationship between endometriosis and various cancers.

What is the potential connection between endometriosis and cancer?

The connection, if any, between endometriosis and cancer is not well understood. Some experts suggest that endometriosis lesions may have similar gene mutations as certain cancers. This could increase the chances of these lesions directly transforming into cancer. However, the possibility of this is incredibly low. Others suggest that endometriosis creates areas of inflammation and increases stress on the body. It may also impact hormone regulation. All of these could contribute to cancer development as well.¹

Researchers do know that some genetic or environmental risk factors may be present in both endometriosis and specific cancers. However, they do not yet have a complete list of what those might be.¹

Researchers have studied trends over time

To learn more about the relationship between endometriosis and cancer, a team of researchers from around the world completed a meta-analysis. This means the researchers went through many past studies and analyzed their results together. In this analysis, the researchers found 49 past studies on endometriosis and various cancer types. They were able to assess how well each study was done and determine how much bias was present. Bias refers to anything in the original study that could affect the results or call into question their accuracy. Ultimately, 49 studies were assessed.¹

The risk of cancer by type

Overall, the researchers found that there was a 7 percent increase in the risk of developing cancer if a person had endometriosis. However, in the grand scheme of all results, this 7 percent was not statistically significant, meaning there may not actually be a meaningful difference overall.¹

Other risks by type of cancer included:¹

• Ovarian cancer – There was a 93 percent increased chance of having ovarian cancer if a person had endometriosis. The most common types of ovarian cancer experienced were clear cell carcinoma and endometrioid carcinoma.
• Thyroid cancer – There was a 39 percent increase in risk of developing thyroid cancer if a person had endometriosis.
• Breast cancer – Only a 4 percent increase in breast cancer risk was observed. This was not statistically significant overall. The most common type of breast cancer reported in past studies for those with endometriosis was ER+/PR- breast cancer (estrogen-sensitive breast cancers).
• Colorectal cancer – Overall, there was no increased risk of developing colon cancer along with endometriosis. However, when looking only at the studies with low bias, there was a 2.29-fold increased risk of developing this type of cancer, suggesting that a link may still be present.
• Endometrial cancer – There was a 23 percent increase in risk of developing endometrial cancer; however, like breast cancer, this was not significant statistically. In fact, the authors suggest that the 23 percent may be an overestimate, as tests used to look for endometriosis may also detect endometrial cancer by coincidence.
• Melanoma – Like colorectal cancer, melanoma did not appear to have a strong relationship with endometriosis overall. However, when looking at only low bias studies, there was a 71 percent increased risk.
• Cervical cancer – Unlike all others, there was a 32 percent decreased risk of developing cervical cancer if a person had endometriosis. The authors suggest that this may be due to people with endometriosis having regular doctor’s appointments and Pap smears, a test used to detect or prevent cervical cancer.

Other cancers mentioned that had no association with endometriosis included, but were not limited to:¹

• Lymphatic and blood cancers
• Lung cancer
• Gastric cancer
• Liver cancer,
• Pancreatic cancer
• Urinary cancer
• Bladder cancer
• Kidney cancer

What does this tell us?

Overall, there needs to be much more research to determine the potential links between each of these cancer types and endometriosis, especially studies that look at time since diagnosis. In some cases, endometriosis and a cancer may be detected at the same time. In other cases, it may take a longer period of time to detect one or the other, even if both are there. This may make it hard to determine which came first (or which led to which), further complicating the potential relationship.¹

Although these results are interesting, the overall risk of developing any of these cancers as a result of endometriosis is still quite low. The authors suggest that these findings should not impact cancer screening. For example, a person should not undergo extra or special screening just because they have endometriosis.¹

Following normal screening guidelines, eating a balanced diet, exercising, and eliminating or reducing other cancer-causing factors (like smoking or heavy alcohol intake) are still some of the strongest ways to prevent cancers in the future.¹