Endometriosis and Ovarian Cancer Risk: What the Data Actually Says | ESSI

Endometriosis and Ovarian Cancer Risk

What the 2024–2025 evidence actually says — and how the ESSI team is thinking about it.

By the ESSI Team · Reviewed by Andrea Vidali, MD · internationalendo.com

For decades, the question of whether endometriosis raises the risk of ovarian cancer has lingered in clinic conversations, often answered with a hedge: “probably, a little, but don’t worry.”

That hedge no longer fits the data. A wave of new evidence — culminating in a 2025 editorial by Bogani and colleagues and a landmark 2024 JAMA cohort by Barnard — has clarified both the size of the signal and, more importantly, who carries it. This post unpacks what those papers actually say, and how we, the ESSI surgical team, are translating them into how we counsel and treat our patients.

AT A GLANCE

• 4.2×: Increased ovarian cancer risk in women with any endometriosis vs. no endometriosis (Barnard, JAMA 2024).

• 9.7×: Risk in women with deep infiltrating endometriosis and/or ovarian endometriomas.

• ~1.1%: Baseline lifetime ovarian cancer risk in U.S. women (SEER) — the number these multiples are scaling.

01 |

The Bogani Editorial: A Clear-Eyed Framing

In May 2025, Giorgio Bogani and colleagues at the Gynecologic Oncologic Unit of Fondazione IRCCS Istituto Nazionale dei Tumori (Milan) published a short editorial in European Journal of Cancer Prevention titled simply “Endometriosis and cancer risk.” It is not a systematic review or a new dataset; it is a concise editorial framing of where the field stands.

The argument the editorial makes is worth repeating in plain language: endometriosis is one of the most common benign gynecologic diseases, but the epidemiology has now matured to the point where a real, reproducible association with ovarian cancer can no longer be waved off. The association is strongest — and most consistent across studies — for the endometrioid and clear cell histotypes. Beyond the ovary, the picture is messier: modest signals appear for endometrial cancer, melanoma, basal cell carcinoma, and non-Hodgkin lymphoma, but the studies disagree, and the effect sizes are small.

Two things make the Bogani editorial useful for clinicians. First, it explicitly names the inconsistency in the broader literature — it does not oversell. Second, it locates the strong signal where it actually lives: in a specific subset of patients, with specific tumor histologies, on a specific carcinogenic pathway. That precision is what allows the editorial to read as honest rather than alarmist.

Clinical Commentary from the Team:

“The Bogani piece does what good editorials should do: it tells you what we know, what we don’t know, and where the noise is. The key sentence — buried in three pages — is that the elevated risk lives in specific histologies, not across the board. Once you accept that, every counseling conversation changes. We are not telling every endometriosis patient that they have a tenfold cancer risk. We are telling a small subset — women with ovarian endometriomas, with deep infiltrating disease, with long disease duration — that they sit on a measurable, identifiable curve. That is a very different conversation, and a much more useful one.” — Andrea Vidali, MD, Founder, ESSI · Gynecologic Surgeon

02 |

Barnard 2024: The Dataset That Changed the Conversation

If the Bogani editorial is the frame, the painting inside it is Barnard et al., published in JAMA on August 13, 2024. Using the Utah Population Database, the investigators matched 78,893 women with surgically or clinically identified endometriosis to a 1:5 ratio of women without endometriosis, and then categorized cases by subtype: superficial endometriosis, ovarian endometriomas, deep infiltrating endometriosis, or other.

The headline numbers are striking and now well-known:

• Women with any endometriosis had a 4.2-fold increased risk of ovarian cancer compared with women without endometriosis.

• Women with ovarian endometriomas and/or deep infiltrating endometriosis had a 9.7-fold increased risk.

• The association was far stronger for Type I ovarian cancers (endometrioid, clear cell, low-grade serous, mucinous) than for Type II (high-grade serous).

Figure 1 — Bar chart illustrating ovarian cancer risk by endometriosis subtype, based on data from Barnard et al., JAMA 2024. Showing the non-linear jump from superficial disease to deep / ovarian disease.

Why the Subtype Distinction Matters More Than the Headline Number

Every prior meta-analysis lumped endometriosis into one bucket and reported a summary risk somewhere between 1.3× and 1.9×. Those numbers are not wrong — they are just averages across a population in which most patients carry minimal risk and a smaller subset carries substantial risk.

The Utah cohort separates them. A woman with isolated superficial peritoneal endometriosis has a risk profile that looks almost nothing like a woman with a 6-cm endometrioma and rectovaginal disease, and the data finally reflect that.

Figure 2 — Horizontal bar chart displaying risk by ovarian cancer histotype. Highlighting that the clear cell signal (~10×) and endometrioid signal (~5×) dominate over the small high-grade serous signal. 

The high-grade serous signal is small and may reflect residual confounding.

Clinical Commentary from the Team:

“When I read the Barnard paper I went back through my own operative log. The patients I had been most aggressive with surgically — the ones with persistent endometriomas, fibrotic deep disease, long histories — are exactly the population the data flag. What changes in clinic? Not panic. What changes is that when I see a 38-year-old with a 5-cm endometrioma she has been watching for six years, I now have a real number to put on the table. We can talk about whether expectant management is still the right answer for her, or whether complete excision has become the right answer not only for her pain but for her long-term risk.” — Madhu Bagaria, MD, Gynecologic Surgeon, ESSI

03 |

Putting the Numbers in Context: Absolute vs. Relative Risk

A 9.7-fold relative risk sounds alarming on its own. It becomes more interpretable when anchored to a baseline.

The lifetime risk of ovarian cancer in U.S. women is roughly 1.1% (SEER). A 9.7-fold multiple scales that to approximately 10–11% lifetime risk — not negligible, but also not the 40–80% figure that comes up in BRCA1/2 conversations.

 Figure 3 — Bar chart displaying estimated absolute lifetime risk of ovarian cancer across the general population, superficial endometriosis (~3.0%), any endometriosis (~4.6%), and deep / ovarian endometriosis (~10.6%).

Individual risk depends heavily on age, family history, parity, and surgical history.

Two caveats deserve emphasis here:

1. These are population-level estimates; an individual patient’s risk is modified by family history, parity, oral contraceptive use, age at diagnosis, surgical history, and disease duration.

2. Ovarian cancer screening with CA-125 and transvaginal ultrasound has not been shown to reduce mortality in average-risk women, and there is no evidence yet that it does so in endometriosis patients either.

The clinical implication is not “screen everyone” — it is “identify the high-risk subset and have a real conversation about it.”

Clinical Commentary from the Team:

“The number that matters in clinic is the absolute risk, not the hazard ratio. A patient walks in and hears “ten times higher” and her stomach drops. We owe her the second sentence: ten times a small number is still a small number, but it is not zero, and here is what we can do about it. For deep endometriosis and persistent endometriomas, excisional surgery is increasingly defensible not just on pain and fertility grounds but on the carcinogenic pathway itself. Removing the lesion removes the iron-rich, chronically inflamed microenvironment in which the ARID1A and PIK3CA hits accumulate.” — Joseph Raccuia, MD, General Surgeon, ESSI

04 |

How Endometriosis Becomes Cancer — The Molecular Arc

The genetic story is now reasonably well-mapped, and it explains why the risk concentrates in specific histotypes.

Figure 4 — Flowchart diagram mapping the molecular arc from eutopic endometrium, to ectopic implant (driven by inflammation, iron, ROS), to atypical endometriosis (driven by ARID1A loss and PIK3CA mutation), and finally to EAOC clear cell / endometrioid histotypes (with PTEN/KRAS/CTNNB1 hits).

The transition is not inevitable — most endometriotic lesions never accumulate the full set of driver mutations. But the chronically inflamed, iron-rich microenvironment of an ovarian endometrioma is uniquely permissive. Endometriotic lesions sit in this hemorrhagic microenvironment, where reactive oxygen species (ROS) from the breakdown of cyclic bleeding generate sustained DNA damage.

Over years, that damage accumulates in the resident epithelium. The first major hit is typically a loss-of-function mutation in ARID1A, a SWI/SNF chromatin-remodeling gene, present in roughly 50% of clear cell carcinomas and a substantial fraction of endometrioid carcinomas. PIK3CA activating mutations frequently co-occur. Subsequent hits in PTEN, KRAS, and CTNNB1 (the latter driving Wnt/β-catenin signaling) complete the transformation. The result is a tumor that retains the genetic fingerprint of its endometriotic origin — hence the term endometriosis-associated ovarian cancer (EAOC).

An intermediate lesion — atypical endometriosis — is increasingly recognized as a histologic marker on the transition curve. Pathologists describing it should be taken seriously. It is not a diagnostic curiosity; it is a flag.

Clinical Commentary from the Team:

“The ARID1A finding is, to me, the single most clinically useful piece of biology in this whole literature. It tells us that the transformation is not random — there is a recognizable molecular path, and most of the early steps happen inside the cyst, in the iron and the inflammation. That changes how I think about endometrioma surgery. Cystectomy with complete capsule excision is not just a fertility-preservation argument anymore. It is an oncologic argument, applied to a much earlier point on the curve than we are used to thinking about.” — Osbert Fernandez, MD, Gynecologic Surgeon, ESSI

05 |

Atypical Endometriosis — Reactive vs. Truly Premalignant

If “atypical endometriosis” was a single thing, this section would be simple. It is not. The term covers two pathologically distinct entities that pathologists have been arguing about since Czernobilsky and Morris first described them in 1979, and the distinction is one of the most clinically consequential things in this whole literature.

[ 📸 INSERT IMAGE 6 HERE: Figure 5 — Infographic table highlighting the two faces of “atypical endometriosis”. Cytologic Atypia (Reactive/Inflammation-driven, intact BAF250a, low premalignant potential) vs. Architectural Atypia (Genuinely premalignant, accumulated genetic hits, BAF250a loss, real bridging lesion to EAOC). ]

Why this matters clinically: when a pathology report reads “atypical endometriosis,” the surgeon and patient deserve to know which kind.

• Cytologic Atypia: Features nuclear enlargement, eosinophilic cytoplasm, and prominent nucleoli in the epithelial lining of an endometriotic cyst. Refining these criteria in 1988, researchers proposed that most of this is reactive atypia — a regenerative response to severe local inflammation and superficial ulceration. In this reading, cytologic atypia is a footprint of the iron-rich, hemorrhagic microenvironment doing what it always does, not a footprint of cancer arriving. A report that specifies cytologic / reactive atypia is generally reassuring — the lesion has been excised, the inflammation removed with it, and there is no specific cancer-precursor signal.

• Architectural Atypia: Features crowded, branching glands with stratification, loss of polarity, and hyperchromatic nuclei. This is the lesion that carries genuine premalignant potential. It looks like accumulating genetic damage. Molecular data shows architectural atypia exhibits loss of BAF250a (ARID1A) at significantly higher rates than typical endometriosis (p = 0.004), lining up with the malignant end of the spectrum. A report specifying architectural atypia warrants completely rethinking the patient’s surveillance schedule, contralateral ovary, and lifetime life-stage options.

Clinical Commentary from the Team:

“I have lost count of how many times I have read “focal atypical endometriosis” on a pathology report and watched a patient panic over what is almost certainly a reactive change to severe inflammation. The pathology language is doing the patient a disservice when it does not specify which kind. I now routinely ask the pathologist three questions: Is this cytologic atypia, architectural atypia, or both? Was BAF250a staining performed? Is there any hyperplastic component? Those three questions take the term “atypical endometriosis” and turn it into actionable information — either reassurance or a real flag.” — Andrea Vidali, MD, Founder, ESSI · Gynecologic Surgeon

06 |

Does Excisional Surgery Actually Lower Ovarian Cancer Risk?

This is the question every endometriosis surgeon wants answered, and the question every patient asks within the first ten minutes of a consult. The short answer: yes, the available evidence points in that direction, although it comes from observational data rather than randomized trials.

The Melin Study — And What It Actually Showed

The most influential evidence comes from Anna-Sofia Melin and colleagues at the Karolinska Institute (2013). They performed a nested case-control study linking national registry records to compare women with both endometriosis and subsequent epithelial ovarian cancer against those with endometriosis but no cancer.

The numbers are striking:

• Unilateral oophorectomy for ovarian endometriosis was associated with an 81% reduction in subsequent ovarian cancer risk (OR 0.19; 95% CI 0.08–0.46).

• Complete surgical excision of all visible endometriosis was associated with a 70% reduction (OR 0.30; 95% CI 0.12–0.74).

• Hormonal therapy alone did not show a comparable signal.

Figure 6 — Bar chart representing surgical interventions and ovarian cancer risk reduction in women with endometriosis. Showing baseline for hormonal treatment/hysterectomy alone vs. substantial risk reductions for complete surgical excision (~70%) and unilateral oophorectomy (~81%). 

What This Means — And What It Does Not Mean

The Melin signal is reinforced by parallel observations: a 2019 cohort following ~830,000 women for 27 years showed that hysterectomy in women with endometriosis reduced subsequent ovarian cancer risk to an HR of 0.17. Tubal ligation, in the broader literature, reduces clear cell and endometrioid ovarian cancer risk by approximately 50%. The 2024 Campbell review explicitly lists “excision of endometriosis” as one of three established risk-reduction strategies alongside tubal ligation and combined hormonal contraception.

Two important caveats apply:

1. The Melin study is observational, not randomized — women who undergo radical excisional surgery may differ systematically from women who do not.

2. Completeness of excision matters. The signal Melin reports is specifically for radical removal of all visible endometriosis — not partial cyst drainage, not ablation, not coagulation of superficial lesions.

The mechanism makes biological sense: if EAOC arises from the chronically inflamed, iron-rich epithelium of an endometriotic lesion, removing that epithelium completely should remove the carcinogenic substrate. Leaving fragments behind does not.

Clinical Commentary from the Team:

“The 70% number from Melin is the single most empowering statistic in this conversation. It reframes the surgery. A complete excision is no longer just “we took out your pain;” it is “we took out the lesion that was, slowly, becoming something else.” But the asterisk matters. Melin’s 70% is for radical removal of all visible disease — not for ablation, not for partial cystectomy, not for the kind of incomplete surgery that leaves microscopic foci behind. The mechanism is straightforward: you cannot remove the carcinogenic substrate if you leave it in.” — Joseph Raccuia, MD, General Surgeon, ESSI

07 |

What We Tell Our Patients: The ESSI Synthesis

Here is how the ESSI team has distilled the current literature into the conversations we have in clinic. None of these statements is original to us — they are direct readings of Bogani 2025, Barnard 2024, Saavalainen 2018, and the broader meta-analytic literature — but the synthesis is ours.

Seven Points for the Clinic Conversation

1. The association is real, but concentrated. Most endometriosis patients carry only a small absolute risk. The signal is concentrated in women with ovarian endometriomas and/or deep infiltrating disease.

2. It is a histotype story. The risk is for Type I tumors — clear cell (~10×) and endometrioid (~5×) — not for the high-grade serous cancers most people picture when they hear “ovarian cancer.”

3. “Atypical endometriosis” is not one thing. Reactive cytologic atypia is largely benign; architectural atypia (especially with ARID1A / BAF250a loss) is the true bridging lesion. Ask the pathologist which kind.

4. Complete excision substantially lowers risk. Melin et al. 2013: ~70% risk reduction with radical excision of all visible disease, ~81% with unilateral oophorectomy for ovarian endometriosis. Ablation and partial cystectomy do not show the same signal.

5. Screening is not the answer. CA-125 and ultrasound have no mortality benefit in average-risk women. We do not recommend reflexive screening for endometriosis patients without other risk factors.

6. Surgical excision has an oncologic case, not just a pain case. For persistent endometriomas and deep infiltrating disease, complete excision removes the iron-rich, inflamed microenvironment in which the ARID1A/PIK3CA hits accumulate.

7. BRCA and family history still matter. Endometriosis-related risk is additive to, not a replacement for, the standard hereditary cancer workup. Family history changes the conversation.

The clinical task is not to alarm every patient with endometriosis. It is to identify the subset on the steep part of the curve — and to act on it surgically, while we still can.

Clinical Commentary from the Team:

“I want to add something about communication. The patient sitting across from you is not reading hazard ratios. She is reading your face. If we deliver this data the way it deserves to be delivered — with the absolute risk first, the subtype distinction second, and the surgical options third — most patients walk out empowered, not frightened. The worst version of this conversation is the one where we hedge so hard that the patient leaves convinced we are hiding something. The Bogani data give us permission to be honest, because we now have honest numbers.” — Daniel Cibulsky, MD, Gynecologic Surgeon, ESSI

“And one last point that doesn’t make it into the papers: the women in front of us in clinic are often the ones who have been dismissed for a decade. Telling them ‘your disease has been quietly accumulating mutations in an ovarian cyst that has been called benign at every prior ultrasound’ is not a comfortable sentence, but it is the truth. What we owe them is not reassurance. It is precision — and the option of a real intervention while the disease is still on the benign side of the curve.” — Andrea Vidali, MD, Gynecologic Surgeon, ESSI

08 |

The Bottom Line

Endometriosis is not a uniform disease, and its relationship to ovarian cancer is not a uniform risk. The 2024–2025 evidence makes one thing clear: in women with ovarian endometriomas and/or deep infiltrating endometriosis, the risk of Type I ovarian cancers — particularly clear cell and endometrioid — is meaningfully elevated.

The mechanism is identifiable, the carcinogenic pathway is reasonably well-mapped, and — most importantly — complete surgical excision substantially lowers later cancer risk. That last point is what changes the conversation. We are not just identifying a population at risk; we have an intervention with a measurable effect size.

Combined with a precise reading of pathology (architectural atypia is not the same as reactive cytologic atypia) and an honest framing of absolute versus relative risk, the ESSI position is straightforward: every endometriosis patient deserves a stratified, individualized risk conversation, and — for the subset on the steep part of the curve — a real surgical option, performed completely, while the disease is still benign.

TALK TO THE ESSI TEAM

• Stratified risk conversations, not generic reassurance.

• If you or your patient has ovarian endometriomas, deep infiltrating endometriosis, or longstanding disease and would like a surgical and oncologic risk review, the ESSI team is available for consultation at internationalendo.com.

REFERENCES

1. Bogani G, Chiappa V, Raspagliesi F, Corso G. Endometriosis and cancer risk. European Journal of Cancer Prevention. 2025 May 1;34(3):276–278. doi:10.1097/CEJ.0000000000000965.

2. Barnard ME, Farland LV, Yan B, Wang J, Trabert B, Doherty JA, et al. Endometriosis Typology and Ovarian Cancer Risk. JAMA. 2024 Aug 13;332(6):482–489. doi:10.1001/jama.2024.9210.

3. Saavalainen L, Lassus H, But A, Tiitinen A, Härkänen T, Gissler M, et al. Risk of gynecologic cancer according to the type of endometriosis. Obstet Gynecol. 2018;131(6):1095–1102.

4. Pearce CL, Templeman C, Rossing MA, Lee A, Near AM, Webb PM, et al. Association between endometriosis and risk of histological subtypes of ovarian cancer: a pooled analysis of case-control studies. Lancet Oncol. 2012;13(4):385–94.

5. Wang C, Liang Z, Liu X, Zhang Q, Li S. The association between endometriosis, tubal ligation, hysterectomy and epithelial ovarian cancer: meta-analyses. Int J Environ Res Public Health. 2016;13(11):1138.

6. Kim HS, Kim TH, Chung HH, Song YS. Risk and prognosis of ovarian cancer in women with endometriosis: a meta-analysis. Br J Cancer. 2014;110(7):1878–1890. doi:10.1038/bjc.2014.29.

7. Somigliana E, Viganò P, Parazzini F, Stoppelli S, Giambattista E, Vercellini P. Association between endometriosis and cancer: a comprehensive review and a critical analysis of clinical and epidemiological evidence. Gynecol Oncol. 2006;101(2):331–341.

8. Sayasneh A, Tsivos D, Crawford R. Endometriosis and ovarian cancer: a systematic review. ISRN Obstet Gynecol. 2011;2011:140310. doi:10.5402/2011/140310.

9. Zafrakas M, Grimbizis G, Timologou A, Tarlatzis BC. Endometriosis and ovarian cancer risk: a systematic review of epidemiological studies. Front Surg. 2014;1:14. doi:10.3389/fsurg.2014.00014.

10. Sarría-Santamera A, Khamitova Z, Gusmanov A, Terzic M, Polo-Santos M, Ortega MA, Asúnsolo A. History of endometriosis is independently associated with an increased risk of ovarian cancer. J Pers Med. 2022;12(8):1337. doi:10.3390/jpm12081337.

11. Wiegand KC, Shah SP, Al-Agha OM, Zhao Y, Tse K, Zeng T, et al. ARID1A mutations in endometriosis-associated ovarian carcinomas. N Engl J Med. 2010;363(16):1532–1543.

12. Anglesio MS, Papadopoulos N, Ayhan A, Nazeran TM, Noe M, Horlings HM, et al. Cancer-associated mutations in endometriosis without cancer. N Engl J Med. 2017;376(19):1835–1848.

13. Melin AS, Lundholm C, Malki N, Swahn ML, Sparén P, Bergqvist A. Hormonal and surgical treatments for endometriosis and risk of epithelial ovarian cancer. Acta Obstet Gynecol Scand. 2013;92(5):546–554. doi:10.1111/aogs.12123.

14. Campbell J, Stewart CJR, Cohen PA. Endometriosis as a risk factor for ovarian cancer: an update on screening, risk reduction, treatment and prognosis. The Obstetrician & Gynaecologist. 2024;26(3):191–199. doi:10.1111/tog.12948.

15. Czernobilsky B, Morris WJ. A histologic study of ovarian endometriosis with emphasis on hyperplastic and atypical changes. Obstet Gynecol. 1979;53(3):318–323.

16. LaGrenade A, Silverberg SG. Ovarian tumors associated with atypical endometriosis. Hum Pathol. 1988;19(9):1080–1084.

17. Stamp JP, Gilks CB, Wesseling M, Eshragh S, Ceballos K, Anglesio MS, et al. BAF250a expression in atypical endometriosis and endometriosis-associated ovarian cancer. Int J Gynecol Cancer. 2016;26(5):825–832.

18. Saavalainen L, Lassus H, But A, Tiitinen A, Härkänen T, Gissler M, et al. A nationwide cohort study on the risk of non-gynecological cancers in women with surgically verified endometriosis. Int J Cancer. 2018;143(11):2725–2731.

METHODOLOGY NOTE: Physician commentary in this article reflects the editorial position of the ESSI surgical team based on the cited literature. Statements are clinical opinion intended for educational purposes and do not constitute individualized medical advice. Patients should discuss their personal risk profile with their treating physician. Charts in Figures 1–3 and Figure 6 are derived from published hazard ratios, odds ratios, and incidence rates; Figures 4 and 5 are schematic representations of the EAOC molecular pathway and the histologic/molecular distinction between cytologic and architectural atypia.