Endometriosis is not cancer. It is a benign condition where tissue similar to the uterine lining grows outside the uterus, causing pain, inflammation, and sometimes fertility problems. However, the relationship between endometriosis and cancer is more nuanced than a simple “no,” which is likely why you’re searching. Endometriosis shares some unsettling biological behaviors with cancer, and it does carry a small increase in risk for certain types of ovarian cancer.
Why Endometriosis Gets Compared to Cancer
Endometriosis behaves in ways that can look surprisingly similar to cancer under a microscope. The cells in endometriosis lesions undergo a process where they lose their normal structure and gain the ability to migrate and invade surrounding tissue. This same process is what allows cancer cells to spread. Researchers noted as far back as the late 1990s that endometriosis cells lose certain protective proteins and gain others in patterns that mirror invasive carcinoma cells.
Endometriosis also stimulates the growth of new blood vessels to feed its lesions, another hallmark of cancer biology. And in rare cases, endometriosis appears at distant sites like the lungs or thighs, potentially traveling through the lymphatic system or bloodstream, which echoes how cancer metastasizes.
Despite these overlaps, there is a critical difference. Endometrial cancer cells grow uncontrollably and form tumors, both within the uterus and potentially in other organs. Endometriosis tissue, while it can invade and spread, does not form tumors and does not exhibit the same runaway, unchecked growth. It responds to hormonal cycles and, while it can cause serious damage to surrounding organs, it lacks the defining feature of malignancy.
The Genetic Overlap
Some of the most striking connections between endometriosis and cancer are at the genetic level. Researchers have found that endometriosis lesions, particularly deep infiltrating lesions, frequently carry mutations in genes called PIK3CA and PTEN. These same mutations are common in ovarian cancer. A single mutation in one of these genes appears to be a normal feature of endometriosis itself, not something that signals danger on its own.
The concern arises when multiple mutations stack up. Endometriosis tissue carrying additional mutations in PIK3CA, PTEN, and a gene called ARID1A is more likely to undergo malignant transformation. In studies of endometriosis-associated ovarian cancers, researchers found the same PIK3CA mutations in both the cancer tissue and the neighboring endometriosis tissue, suggesting the cancer grew directly from the endometriosis. In one study, 86% of non-atypical endometriosis samples that were found alongside ovarian cancer had already lost normal ARID1A function.
This does not mean endometriosis routinely becomes cancer. It means the two conditions share a genetic neighborhood, and in a small number of cases, the disease can take a wrong turn.
How Much Does Endometriosis Raise Cancer Risk?
The overall lifetime risk of endometriosis transforming into cancer is estimated at 1 to 3%, according to data cited by the American Society of Clinical Oncology. To put that differently: 97 to 99% of people with endometriosis will never develop a related cancer.
A study highlighted by the National Institutes of Health found that women with endometriosis had about four times the risk of ovarian cancer compared to women without it. In practical terms, that translated to roughly 10 additional cases per 10,000 women. The risk was not spread evenly across all types of endometriosis. Women with more severe subtypes, specifically deep infiltrating endometriosis and ovarian endometriomas (cysts on the ovary), had more than nine times the risk of women without endometriosis.
The cancers most closely linked to endometriosis are two specific subtypes of ovarian cancer: clear cell carcinoma and endometrioid carcinoma. These are distinct from the most common type of ovarian cancer (high-grade serous carcinoma), and they tend to be diagnosed at earlier stages.
What Screening Looks Like
You might expect that a diagnosis of endometriosis would come with regular cancer screening, but current medical guidelines say otherwise. The 2024 Korean Society of Endometriosis guidelines, consistent with international recommendations, state that women with endometriosis should not undergo additional cancer testing beyond what is already recommended for the general population. The risk, while elevated relative to the general population, is still low enough that routine extra screening is not considered beneficial for most people.
The exception is for individuals who have additional risk factors, such as a family history of ovarian cancer or known genetic mutations. In those cases, doctors may recommend individualized surveillance.
One reason blanket screening is difficult is that the tools available are not very precise. The CA-125 blood test, often associated with ovarian cancer detection, is elevated by many noncancerous conditions, including endometriosis itself, menstruation, uterine fibroids, and pregnancy. A high CA-125 level in someone with endometriosis does not necessarily signal cancer, and the test is not accurate enough to be used as a general screening tool.
What This Means in Practice
If you have endometriosis, the most important takeaway is that your condition is not cancer and is unlikely to become cancer. The biological similarities are real and actively studied, but they represent shared cellular mechanisms, not a shared diagnosis. Endometriosis is a chronic inflammatory condition. Cancer is uncontrolled malignant growth. The two can coexist and, in rare cases, one can lead to the other, but they are fundamentally different diseases.
The subgroup that warrants closer attention includes people with ovarian endometriomas or deep infiltrating disease, particularly those with a family history of ovarian or endometrial cancer. If you fall into that category, it is reasonable to discuss your individual risk profile with a gynecologist who specializes in endometriosis. For the vast majority of people with endometriosis, the focus of care remains on managing pain, preserving fertility, and improving quality of life.