Endometriosis is not a type of cancer. It is classified as a benign gynecological condition in which tissue resembling the uterine lining grows in places it does not belong, such as the ovaries, fallopian tubes, and pelvic lining. But calling it “benign” undersells how much it has in common with malignancy at the cellular level, and the question is less absurd than it might sound. Endometriotic cells invade surrounding tissue, recruit their own blood supply, resist normal cell death, and sometimes carry mutations in the very genes that drive cancer.
Why the Comparison Keeps Coming Up
If you listed the hallmarks of cancer on a whiteboard and then listed the behaviors of endometriotic tissue next to them, the overlap would be striking. Cancer cells invade neighboring tissue, build new blood vessels to feed themselves, dodge the immune system, and resist the signals that tell normal cells to die. Endometriotic cells do many of these same things, just without the runaway, life-threatening proliferation that defines a malignant tumor.
One of the clearest parallels is angiogenesis, the process of sprouting new blood vessels. For an endometrial implant to survive after landing on, say, the peritoneal lining, it needs a blood supply. Endometriotic cells produce vascular endothelial growth factor (VEGF), a potent signal that drives the formation of new vessels from existing ones.1PubMed Central. Angiogenesis and Endometriosis After the tissue attaches, high VEGF levels increase the surrounding blood vessel network and help the implant establish itself.2PubMed. Vascular endothelial growth factor in endometriosis This is essentially the same trick tumors use to grow beyond a few millimeters in size.
Endometriotic tissue also remodels the surrounding structural framework in ways that mirror tumor invasion. It uses proteolytic enzymes to break down and reshape the tissue matrix, allowing implants to grow, invade deeper, and form adhesions.3PubMed Central. Matrix remodeling and endometriosis Another cancer-like behavior is epithelial-to-mesenchymal transition, a process where cells shed their normal architecture and acquire the ability to migrate. Researchers believe this transition is one of the prerequisites for endometriotic lesions to establish themselves in new locations.4PubMed Central. Epithelial-to-mesenchymal transition in the development of endometriosis
On top of all that, endometriotic cells appear to resist apoptosis, the programmed self-destruct sequence that normally clears out cells that have ended up where they shouldn’t be. Dysregulation of multiple cell-death pathways, including apoptosis and a newer-studied process called ferroptosis, has been linked to how endometriosis develops and persists.5PubMed Central. Regulated Cell Death in Endometriosis When the body’s cleanup crew fails, displaced tissue gets a chance to take root.
The Immune System’s Role
A healthy immune system should, in theory, clear endometrial cells that end up outside the uterus. During menstruation, small amounts of tissue flow backward through the fallopian tubes into the pelvic cavity. This happens in most women, yet only a fraction develop endometriosis. One reason is immune dysfunction. Research has shown that neutrophils, macrophages, natural killer cells, and dendritic cells all behave abnormally in the endometriosis environment, and instead of attacking the misplaced tissue, they sometimes help it grow by releasing signals that promote blood vessel formation and cell invasion.6PubMed Central. The Role of the Immune System in the Development of Endometriosis This immune evasion is another hallmark shared with cancer, but the outcome is fundamentally different: the tissue establishes itself without becoming a tumor.
Cancer Driver Mutations in Non-Cancerous Tissue
Perhaps the most unsettling overlap is genetic. When researchers sequenced the DNA of endometriotic lesions in patients who did not have cancer, they found somatic mutations, changes acquired over a cell’s lifetime rather than inherited, in roughly four out of five patients. Some of those mutations were in well-known cancer driver genes such as KRAS, ARID1A, PIK3CA, and PPP2R1A.7PubMed Central. Cancer-Associated Mutations in Endometriosis without Cancer These are the same genes found mutated in ovarian cancer, endometrial cancer, and other malignancies.
A growing body of evidence confirms that these mutations are recurrent across endometriosis patients and may play a role in how the disease starts and progresses, rather than being random bystanders.8F&S Reviews. The role of somatic mutations in endometriosis: pathogenesis, progression, and fibrogenesis This finding was genuinely surprising when it first emerged. Having a cancer driver mutation does not mean you have cancer, clearly, since people walk around with such mutations in skin cells, blood cells, and other tissues without ever developing a malignancy. But it does raise the question of what, exactly, keeps endometriosis from crossing the line.
The honest answer is that researchers are still working that out. The prevailing thinking is that endometriosis lacks the full cascade of mutations, chromosomal instability, and loss of growth-limiting controls that characterize a true malignancy. It may be stuck in what some scientists describe as a “premalignant” zone, sharing some genetic features with cancer but missing the final steps needed for uncontrolled, invasive growth and the ability to metastasize to distant organs.
How Much Does Endometriosis Raise Cancer Risk?
This is the question that matters most practically, and the answer is: yes, there is a measurable increase in risk, but it is far smaller than most patients fear. A large study analyzing nearly 180,000 endometriosis patients found an overall cancer risk roughly a third higher than controls.9PubMed. Markedly increased risk of malignancies in women with endometriosis The most elevated risks were for uterine cancer (about four and a half times higher), ovarian cancer (about two and a half times higher), and cervical and breast cancer at more modest elevations.
A nationwide Scandinavian cohort study found similar patterns but with somewhat smaller magnitudes: an increased ovarian cancer risk driven primarily by the clear-cell subtype (about three and a half times the expected rate) and the endometrioid subtype, plus a modest increase in endometrial cancer.10PubMed. Endometriosis and risks for ovarian, endometrial and breast cancers: A nationwide cohort study A UK national cohort also confirmed a higher ovarian cancer risk, roughly 75% above the comparison group.11PubMed. Impact of endometriosis on risk of further gynaecological surgery and cancer: a national cohort study
Numbers like “two and a half times the risk” sound alarming out of context. But ovarian cancer is relatively uncommon to begin with. A woman’s lifetime risk of ovarian cancer is around 1 to 1.5 percent. Even doubling or tripling that risk keeps the absolute number low. The vast majority of people with endometriosis will never develop an associated cancer. Still, the elevated risk is real enough that clinicians take it seriously, especially for the clear-cell and endometrioid subtypes of ovarian cancer.
When Endometriosis Does Become Malignant
In rare cases, cancer arises directly within an endometriotic lesion. When that happens, about 80% of the time the malignancy is in the ovary, while the remaining 20% shows up in locations like the intestines, rectovaginal septum, abdominal wall, or even the lining around the lungs.12PubMed Central. Endometrioid Carcinoma Arising from an Endometriosis-Associated Abdominal Wall Scar A case series of ten patients with malignant extra-ovarian endometriosis found tumors centered in the pelvis, broad ligament, and rectovaginal septum, with the most common type being endometrioid adenocarcinoma, followed by clear cell carcinoma and adenosarcoma.13PubMed. Malignant extra-ovarian endometriosis: A case series of ten patients and review of the literature
The molecular pathway from endometriosis to ovarian clear cell carcinoma is among the best-studied transformation routes. Research has identified mutations in ARID1A and PIK3CA, along with activation of specific proteins like HNF-1β, as playing roles in that transition.14PubMed Central. Endometriosis-associated Ovarian Clear Cell Carcinoma: A Special Entity? Other molecular studies have found that the tumor suppressor PTEN is lost early on, in both the endometriosis itself and the invasive tumor, suggesting the malignant change builds on a foundation already laid in the benign disease.15PubMed Central. Molecular changes in endometriosis-associated ovarian clear cell carcinoma
The Diagnostic Challenge
One of the practical headaches in clinical care is that endometriosis and certain ovarian cancers can look similar on imaging and blood tests. CA125, the blood marker most commonly associated with ovarian cancer screening, is frequently elevated in endometriosis patients as well because pelvic inflammation drives it up.16Journal of Ovarian Research. Systemic immune and coagulation amplifiers resolve diagnostic ambiguity in endometriosis-associated ovarian cancer If your doctor orders a CA125 test and it comes back high, that alone does not tell you whether you are dealing with endometriosis, cancer, or both.
Researchers have found that adding other biomarkers helps. In one study, a marker called HE4 was never elevated in patients with endometriosis or other benign masses but was consistently elevated in ovarian cancer patients. Another marker, CA72-4, also showed a strong difference between endometriosis and cancer.17PubMed Central. The use of HE4, CA125 and CA72-4 biomarkers for differential diagnosis between ovarian endometrioma and epithelial ovarian cancer CT imaging features such as the number of cysts, the growth pattern of any solid nodules within a cyst, and the presence of fluid in the abdomen also help distinguish between malignant and benign endometriosis-related masses.18PubMed. Assessing CT imaging features combined with CEA and CA125 levels to identify endometriosis-associated ovarian cancer
For patients, the important takeaway is that a raised CA125 level in the context of known endometriosis is not an automatic reason for panic. Clinicians are increasingly combining multiple markers and imaging characteristics to sort out what is going on, rather than relying on CA125 alone.
Treatments That Cross the Line
Another reason people wonder about the cancer connection is that some treatments overlap. Medications originally developed for estrogen-dependent cancers have found applications in treating endometriosis and the related condition adenomyosis, because the three conditions share features at the molecular level.19PubMed Central. Shared Pathogenic and Therapeutic Characteristics of Endometriosis, Adenomyosis, and Endometrial Cancer: A Comprehensive Literature Review More broadly, many anti-cancer drugs have shown therapeutic potential for endometriosis in cell, animal, and clinical studies.20PubMed. Anti-cancer Drugs in Endometriosis Management: Mechanisms and Therapeutic Potential
This does not mean endometriosis is being treated “as if it were cancer.” It means that when two diseases hijack similar biological pathways, a drug that blocks one of those pathways might work for both. Hormonal suppression, for instance, starves both estrogen-driven tumors and endometriotic implants of the fuel they need to grow. Anti-angiogenic agents that cut off blood vessel formation in tumors could, in principle, do the same thing to endometriotic lesions. The shared toolbox of treatments reflects shared biology rather than shared identity.
How Endometriosis Spreads
Endometriosis can appear in surprisingly distant locations, including the lungs, diaphragm, and even the brain in extremely rare cases. This has led some researchers to draw parallels with metastasis. The dominant explanation for most pelvic endometriosis is retrograde menstruation, where fragments of uterine lining travel backward through the fallopian tubes. But this does not easily explain lesions in faraway sites.
One theory that does account for distant spread involves the lymphatic system. Endometrial and endometriotic tissue has been found in lymphatic vessels and lymph nodes, and lymphatic dissemination has been proposed as an explanation for both rare-site endometriosis and the high recurrence rates seen after treatment.21Biology of Reproduction. The Role of the Lymphatic System in Endometriosis: A Comprehensive Review of the Literature Another line of research points to stem-like progenitor cells that may contribute to lesion formation. Stem cell markers have been found at significantly higher levels in endometrial tissue from endometriosis patients compared with healthy women, suggesting these cells may seed new lesions in the peritoneal cavity.22Genes & Diseases. Endometrial stem/progenitor cells: Properties, origins, and functions – Section: Endometriosis
These mechanisms sound a lot like how cancer spreads, and in a purely mechanical sense, they are similar: cells traveling through lymph or blood to colonize new territory. The critical difference is that endometriotic implants, while invasive and destructive to surrounding tissue, do not exhibit the uncontrolled proliferation and genetic chaos of metastatic cancer cells. They grow, they persist, they cause enormous suffering, but they do not form aggressive tumors that threaten organ function in the way a metastatic cancer does.
The Psychological Weight of “Is This Cancer?”
The fear that endometriosis might be or become cancer is part of a broader pattern of psychological distress in people living with the disease. Research into how endometriosis affects mental health has identified disruption as a central theme: disruption to daily life, to fertility plans, to identity, and to trust in the medical system. A long and often frustrating diagnostic journey, poor doctor-patient relationships, and a lack of social support all contribute to higher distress.23PubMed. “Free butterflies will come out of these deep wounds”: A grounded theory of how endometriosis affects women’s psychological health
Being told your condition shares genetic features with cancer, or that your CA125 is elevated, or that you have a moderately higher risk of ovarian cancer, can feed directly into that distress. Context matters when receiving those facts. The absolute risk of developing cancer remains low, even with endometriosis. And the shared biological features between the two conditions, far from being a source of dread, are actually opening new treatment pathways. Each new overlap that researchers identify between endometriosis and cancer biology is a potential therapeutic target, not just a scary headline.
Endometriosis in Younger Women and Global Patterns
Endometriosis is most common in women aged 20 to 34, with a peak between 25 and 29.24BMC Public Health. The global burden of polycystic ovary syndrome, endometriosis, uterine fibroids, cervical cancer, uterine cancer, and ovarian cancer from 1990 to 2021 Global burden data also reveal that lower-income regions carry higher incidence and prevalence rates for endometriosis, while higher-income regions see more of the cancers associated with it, such as ovarian and uterine cancer. This pattern likely reflects differences in diagnostic access and the average age at which endometriosis is caught, along with the demographic and lifestyle factors that influence cancer rates differently across populations.
For younger patients in particular, the cancer question feels distant and somewhat abstract, which is appropriate. The immediate concerns with endometriosis in your twenties and thirties are pain management, fertility preservation, and quality of life. The cancer risk, while worth knowing about, becomes more relevant as a topic for long-term surveillance and conversations with a gynecologist over time rather than something demanding urgent action at diagnosis.
Historical Neglect of the Disease
Part of the reason patients end up anxiously searching “is endometriosis cancer” in the first place is that the disease has been poorly understood and under-researched for most of medical history. Scholars have drawn connections between endometriosis and historical descriptions of “hysteria,” the catch-all diagnosis once applied to women with unexplained pelvic pain, emotional distress, and reproductive problems. Some researchers have argued that if even a fraction of historical hysteria cases were actually undiagnosed endometriosis, it would represent one of the largest mass misdiagnoses in medical history, one that subjected women to centuries of stigma, institutionalization, and untreated pain. That legacy of dismissal has left endometriosis research chronically underfunded relative to how common and debilitating the condition is, and it has left patients without the clear, confident answers they deserve about what their disease is and what it is not.