Endometriosis and Cancer Risk: What the Science Actually Says

Endometriosis is not cancer. However, growing scientific evidence shows that it shares certain biological features with cancer. These similarities help explain why endometriosis can be persistent, painful, and difficult to treat.

Importantly, sharing biological behaviors does not make endometriosis malignant.

Shared Biological Behavior

It is well established that endometriosis lesions can grow outside their original uterine lining tissue and implant on organs beyond the uterus—including, in some cases, areas outside the pelvic cavity.

Endometriosis lesions can also:

  • Promote angiogenesis (formation of new blood vessels), allowing lesions to implant and survive

  • Promote neurogenesis (growth of new nerve fibers), contributing to pain

  • Produce their own estrogen locally, allowing continued local growth

  • Persist in a state of chronic inflammation and immune system dysregulation

Together, these processes create a self-sustaining cycle:

  • Inflammation promotes lesion growth

  • Lesion growth drives further inflammation

These biological features are also observed in cancer biology. However, this does not mean endometriosis behaves as a malignant disease.

Key Differences from Cancer

Despite these similarities, critical differences exist:

  • Endometriosis lesions are considered benign

  • They do not metastasize through the blood or lymphatic systems like cancer

  • Tissue damage occurs through:

    • Chronic inflammation

    • Fibrosis and scarring

    • Nerve involvement

  • Damage is not caused by rapid, uncontrolled malignant cell division

Understanding this distinction is essential.

The Link to Ovarian Cancer

The most consistently observed association between endometriosis and cancer involves certain subtypes of ovarian cancer, referred to as endometriosis-associated ovarian cancer (EAOC).

EAOC most commonly involves specific subtypes:

  • Clear cell ovarian carcinoma

  • Endometrioid ovarian carcinoma

Studies suggest that women with endometriosis have approximately a 1.3 to 1.9 times increased relative risk of developing these specific ovarian cancer subtypes compared with women without endometriosis.

Important Context

  • The absolute risk remains low

  • The vast majority of individuals with endometriosis will not develop ovarian cancer

  • Endometriosis does not mean cancer is inevitable

EAOC is thought to develop in the setting of long-standing endometriosis, particularly within ovarian endometriomas (often called “chocolate cysts”). These cysts contain old blood rich in breakdown products, which may increase oxidative stress and potentially contribute to DNA damage over time.

Other Investigated Cancer Associations

Research has explored potential associations between endometriosis and other cancers:

Weak to moderate associations reported:

  • Thyroid cancer

  • Endometrial cancer (cancer of the uterine lining)

Less consistent findings:

  • Breast cancer

  • Colorectal cancer

Overall, findings vary and do not imply direct causation.

Given the low and uncertain associations, general cancer prevention recommendations remain relevant for everyone, including:

  • Avoiding smoking

  • Maintaining a healthy weight

  • Staying physically active

  • Eating a balanced diet

  • Limiting alcohol consumption

  • Practicing sun protection

Neurogenesis and Pain Amplification

Another way endometriosis behaves similarly to tumor biology is through its interaction with nerves.

Research shows that endometriosis lesions can promote the growth of new sensory and autonomic nerve fibers. This process—called neurogenesis—may contribute to:

  • Central sensitization

  • Persistent, amplified pain

The close interaction between nerve growth, tissue invasion, inflammation, and hormonal signaling helps explain:

  • Why pain severity does not always correlate with lesion size or stage

  • Why symptoms may persist even after hormonal treatment

Why Isn’t Chemotherapy Used?

If endometriosis shares biological features with cancer, it is reasonable to ask whether cancer treatments like chemotherapy might help.

However:

  • Endometriosis lesions are benign

  • They do not consist of rapidly dividing malignant cells

  • Chemotherapy targets rapidly dividing cancer cells

Current human evidence is extremely limited. Expert consensus indicates that the toxicity and long-term risks of chemotherapy outweigh any theoretical benefit in endometriosis.

For this reason, chemotherapy has no role in standard endometriosis care.

Management typically focuses on:

  • Hormonal modulation

  • Surgical excision when appropriate

Why This Matters

Endometriosis lesions can behave similarly to tumor tissue in some biological respects. This may help explain:

  • The wide range of symptoms patients experience

  • Why endometriosis is not “just bad periods”

  • Why it can be so persistent and difficult to treat

It is completely valid to feel unsettled when first learning about these associations. But understanding them is not about creating fear—it is about scientific accuracy and patient empowerment.

Greater research funding is urgently needed. Understanding these mechanisms may:

  • Inform future clinical guidelines

  • Support earlier diagnosis

  • Encourage development of prevention strategies

  • Improve long-term outcomes

Knowledge is not fear—it is power.

References
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 Bulun SE et al. Endometriosis. Endocr Rev. 2019;40(4):1048–1079.
 Vercellini P et al. Endometriosis: pathogenesis and treatment. Nat Rev Endocrinol. 2014;10(5):261–275.
 Pearce CL et al. Association between endometriosis and risk of histological subtypes of ovarian cancer. Lancet Oncol. 2012;13(4):385–394.
 Saavalainen L et al. Risk of gynecologic cancer according to the type of endometriosis. Obstet Gynecol. 2018;131(6):1095–1102.
 Anglesio MS et al. Endometriosis-associated ovarian cancers. Clin Obstet Gynecol. 2017;60(4):711–727.
 Nezhat FR et al. New insights in the pathophysiology of ovarian cancer. Am J Obstet Gynecol. 2015;213(3):262–267.
 Tokushige N et al. Nerve fibres in peritoneal endometriosis. Hum Reprod. 2006;21(11):3001–3007.
 McKinnon BD et al. Inflammation and nerve fiber interaction in endometriotic pain. Trends Endocrinol Metab. 2015;26(1):1–10.
 Kvaskoff M et al. Endometriosis and cancer: a systematic review and meta-analysis. Hum Reprod Update. 2021;27(2):393–420.
 Mitranovici M-I et al. Shared Pathogenic and Therapeutic Characteristics of Endometriosis, Adenomyosis, and Endometrial Cancer. Pharmaceuticals (Basel). 2024;17(3):311.
 Neykhonji M et al. Anti-cancer Drugs in Endometriosis Management: Mechanisms and Therapeutic Potential. Curr Pharm Des. 2025 Aug 7. doi:10.2174/0113816128387356250720042300.

Consensus.app was used to assist in summarizing current scientific consensus and literature on endometriosis, neurogenesis, and cancer risk.

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Endometriosis Comorbidities: A Whole-Body Disease