Endosalpingiosis is classified as a benign condition, but its relationship with cancer is more complicated than that label suggests. Large studies have found that women with endosalpingiosis are diagnosed with gynecologic cancers at roughly double the rate of women with endometriosis, and molecular research has uncovered shared cancer-driving mutations in endosalpingiotic tissue and adjacent tumors. Whether endosalpingiosis actively contributes to cancer development or simply tends to appear alongside it remains an open question, but the association is strong enough that it has changed how pathologists and surgeons think about this once-dismissed finding.
What Endosalpingiosis Actually Is
Endosalpingiosis occurs when tissue that looks and behaves like the lining of the fallopian tube shows up somewhere it does not belong. The displaced tissue forms small, fluid-filled cysts or glandular structures, most often on the peritoneum (the membrane lining the abdomen and pelvis), on the surface of the ovaries, or inside pelvic lymph nodes. Unlike endometriosis, which involves misplaced uterine lining and tends to cause pain, bleeding, and inflammation, endosalpingiosis is usually quiet. Many people never know they have it.
The condition belongs to a family of four related developmental disorders collectively called müllerianosis. The underlying idea is that during fetal development, müllerian tissue (the embryonic precursor to the uterus, fallopian tubes, and cervix) can end up in the wrong location, where it persists into adulthood.1PubMed. Müllerianosis: four developmental (embryonic) mullerian diseases The other three conditions in this group are endometriosis, endocervicosis (displaced cervical tissue), and adenomyosis (uterine lining growing into the uterine muscle wall). Of the four, endosalpingiosis has historically received the least attention, partly because it rarely causes symptoms on its own.
In a retrospective study of 16 cases, about a third of women with endosalpingiosis had pelvic pain, another third had menstrual problems, and the remaining third had no complaints at all.2PubMed. Endosalpingiosis-an underestimated cause of chronic pelvic pain or an accidental finding? A retrospective study of 16 cases That last group is telling: for many women, endosalpingiosis is discovered only because a surgeon was already operating for a different reason.
More Common Than Previously Believed
For decades, textbooks treated endosalpingiosis as rare. That impression came from an era when pathologists did not routinely section fallopian tubes and ovaries with the thoroughness now standard. When researchers at one center applied a detailed tissue-examination protocol to surgical specimens, they found endosalpingiosis in about 22% of patients, a rate far higher than older estimates.3PubMed Central. Prevalence of endosalpingiosis and other benign gynecologic lesions The same study found that benign gynecologic lesions of at least one type were nearly universal in women over age 50, present in 93% of that group. Unlike endometriosis, which peaked around menopause and then dropped, endosalpingiosis continued to increase with age. That pattern matters because it means endosalpingiosis is still present and potentially accumulating changes in the years when ovarian and uterine cancers become more common.
The Statistical Link to Gynecologic Cancer
The most direct evidence connecting endosalpingiosis to cancer comes from studies comparing women who have the condition with those who do not. In a large analysis, women with endosalpingiosis had a cancer diagnosis at the time of surgery roughly 40% of the time, compared with about 18% for women with endometriosis. Even after excluding patients who were already known or suspected to have cancer before surgery, the gap held: about 21% versus 6%.4PubMed. The association of endosalpingiosis with gynecologic malignancy After adjusting for age and other factors, having endosalpingiosis was associated with roughly two and a half times the odds of a concurrent cancer diagnosis and a higher risk of death.
A separate study from a gynecologic surgery consortium found that women with endosalpingiosis were significantly more likely to have uterine cancer and ovarian cancer compared to women without it. When the researchers focused specifically on ovarian cancer subtypes, serous borderline tumors were about ten times more common in women with endosalpingiosis, and clear cell and mucinous tumors were also elevated.5Gynecologic Oncology. Endosalpingiosis: More than just an incidental finding at the time of gynecologic surgery? These associations persisted after accounting for age, race, menopausal status, prior tubal ligation, and coexisting endometriosis.
A systematic review of the surgical literature found that among patients with endosalpingiosis, roughly 9% had a malignancy somewhere. Ovarian tumors accounted for about a fifth of those, uterine cancers about a third, and breast cancers about 17%.6PubMed Central. Intraoperative Appearance of Endosalpingiosis: A Single-Center Experience of Laparoscopic Findings and Systematic Review of Literature The same review noted that gynecologic malignancies appeared alongside endosalpingiosis in nearly 29% of the single-center cases they examined.
Shared Mutations Suggest a Biological Connection
Association does not prove causation. Endosalpingiosis could simply be common in the same population of women who develop cancer for unrelated reasons, or it could share something deeper with the tumors growing nearby. Molecular studies have started to tilt the evidence toward a shared biology.
In a study of 21 women who had both endosalpingiosis and an ovarian low-grade serous tumor (either at the same time or years apart), researchers looked for cancer-driving mutations in the endosalpingiotic tissue itself. They found mutations in about half of the women. In the vast majority of those cases, the mutations in the endosalpingiosis were identical to those in the tumor.7PubMed Central. Oncogenic BRAF and KRAS mutations in endosalpingiosis The mutations involved BRAF and KRAS, two genes that are well-established drivers of cell growth in many cancers. Finding these same mutations in tissue that looks benign under the microscope suggests that endosalpingiosis may, in some women, represent an early or pre-cancerous step in the development of low-grade serous ovarian tumors.
This does not mean every patch of endosalpingiosis is destined to become cancer. Most will not. But the finding challenges the longstanding assumption that endosalpingiosis is simply inert tissue that happens to be in the wrong spot. At least some endosalpingiotic lesions carry the same molecular machinery that drives malignant growth.
Immunohistochemistry Ties Endosalpingiosis to the Fallopian Tube and to Serous Tumors
Separate from the mutation work, researchers have examined how endosalpingiotic tissue behaves at the protein level. In a study of tissue removed during preventive surgeries, endosalpingiosis was found in about 3.5% of specimens. When the researchers stained the tissue for various markers, the endosalpingiotic cells closely resembled normal fallopian tube lining and looked nothing like the surface of the ovary.8Gynecologic Oncology. Endosalpingiosis as it relates to tubal, ovarian and serous neoplastic tissues: an immunohistochemical study of tubal and Müllerian antigens Three specific protein markers were shared between endosalpingiosis, normal fallopian tube tissue, and serous tumors but were absent in normal ovarian surface tissue and in other tumor types.
This matters because a leading theory in ovarian cancer research holds that many “ovarian” serous cancers actually originate from the fallopian tube. If endosalpingiosis is essentially fallopian tube tissue scattered across the pelvis, and if it shares molecular markers with serous tumors, it fits neatly into that theory as a potential intermediate step. The tissue has the right identity and, as the mutation studies show, sometimes the right genetic alterations to progress toward malignancy.
A Documented Case of Malignant Transformation
There is at least one reported case in which cancer appeared to arise directly within endosalpingiotic tissue. A patient with widespread cystic endosalpingiosis involving the omentum, peritoneum, and retroperitoneum was found to have a focus of serous adenocarcinoma developing inside one of the cysts.9Journal of Clinical Pathology. Serous adenocarcinoma of the sigmoid mesentery arising in cystic endosalpingiosis A single case report cannot establish how often this happens, but it provides concrete proof-of-concept that malignant transformation within endosalpingiotic tissue is possible, not just theoretical.
When Endosalpingiosis Mimics Cancer
Beyond the question of whether endosalpingiosis contributes to cancer development, it creates a separate clinical problem: it can look like cancer even when it is not. This mimicry plays out in several settings.
Lymph Node Involvement
When surgeons remove lymph nodes during cancer staging operations, pathologists sometimes find small glandular structures inside the nodes that look remarkably like metastatic tumor deposits. In one reported case, a woman undergoing a hysterectomy and lymph node removal for endometrial cancer was found to have glandular tissue in her pelvic lymph nodes. There was no actual cancer spread; the tissue turned out to be benign müllerian-type inclusions consistent with endosalpingiosis.10Cancer Research and Treatment. Müllerian-Type Gland Inclusions in Pelvic Lymph Nodes Mimicking Metastasis: A Case Report and Review of the Literature If a pathologist mistakes these inclusions for metastatic cancer, the patient could be incorrectly upstaged, potentially leading to unnecessary chemotherapy or radiation. The opposite error, dismissing real metastasis as benign inclusions, is equally dangerous. Awareness of this diagnostic trap is essential for accurate cancer staging.
Elevated CA-125
CA-125 is a blood protein commonly used as a marker for ovarian cancer. But endosalpingiosis can raise CA-125 levels substantially without any malignancy present. One documented case involved a 46-year-old woman with abdominal swelling, leg swelling, weight loss, and a CA-125 level of 287 (normal is usually under 35). Everything pointed toward advanced cancer. She underwent extensive surgery including removal of her uterus, ovaries, and part of the omentum. No cancer was found. The final diagnosis was disseminated cystic endosalpingiosis.11World Journal of Pharmaceutical Research. ASCITES AND ELEVATED VALUES OF TUMOR MARKER CA 125 IN DISSEMINATED ENDOSALPINGIOSIS Cases like this highlight why a high CA-125 alone should never be taken as proof of malignancy.
Imaging Confusion
On ultrasound, CT, or MRI, endosalpingiosis can form masses that look suspicious. When it occurs in the uterus, it has been mistaken for a degenerating fibroid. One case involved a 31-year-old woman whose imaging suggested a uterine fibroid with cystic changes; the correct diagnosis was made only after surgery.12PubMed. Uterine endosalpingiosis: Case report and review of the literature The authors noted that many patients in the published literature ended up with hysterectomies, raising the possibility that some were overtreated for a benign process that might have been managed more conservatively if it had been recognized preoperatively.
Endosalpingiosis Outside the Reproductive Organs
Although the pelvis is by far the most common location, endosalpingiosis occasionally turns up in unexpected places. The urinary bladder is the best-documented extra-gynecologic site. A literature review identified 27 cases of müllerianosis affecting the bladder and three affecting the lower ureter.13PubMed. Müllerianosis, Endocervicosis, and Endosalpingiosis of the Urinary Tract: A Literature Review In these cases, the tissue typically forms a polyp or mass protruding into the bladder, which on imaging is indistinguishable from bladder cancer.14PubMed Central. Endosalpingiosis of urinary bladder: report on a rare entity One such case was initially worked up as a probable bladder tumor before tissue biopsy revealed benign endosalpingiotic glands.15PubMed Central. Müllerianosis of the urinary bladder may simulate a bladder cancer: a case report
Bladder endosalpingiosis is rare enough that most urologists will never encounter it, but when it does appear, the clinical path almost always runs through a cancer scare before the pathology comes back benign. This reinforces a broader point: tissue biopsy is the only reliable way to distinguish endosalpingiosis from malignancy, regardless of where it shows up.
What Clinicians and Patients Should Take from All This
The relationship between endosalpingiosis and cancer sits in an uncomfortable middle zone. The epidemiologic data consistently shows a real statistical association, and the molecular data provides a plausible mechanism. But no one has demonstrated that treating or removing endosalpingiosis prevents cancer, and the vast majority of endosalpingiotic tissue never progresses. There are no screening guidelines specific to endosalpingiosis and no consensus on whether an incidental finding of endosalpingiosis should change how a patient is monitored.
For a patient told that endosalpingiosis was found during surgery, the practical takeaway is nuanced. The condition itself is benign. But given the statistical associations, it is reasonable to have an informed conversation with a gynecologist about whether any additional follow-up makes sense, especially if the tissue was found alongside other concerning pathology or if there is a family history of ovarian or uterine cancer. Some clinicians have suggested that endosalpingiosis may eventually be recognized as a precursor lesion, similar to how certain types of polyps are viewed in colon cancer, but that framework is not yet established.
Why the Research Has Been Slow
Endosalpingiosis has been recognized for nearly a century. The concept traces back to the 1920s, when John Sampson published foundational work describing both endometriosis and endosalpingiosis as displaced müllerian tissue. Despite that long history, the condition has lived in the shadow of endometriosis, which causes far more obvious symptoms and has attracted far more research funding and clinical attention. Endosalpingiosis was long treated as a histologic curiosity, something a pathologist might note on a report but that rarely influenced clinical decisions.
The recent shift in interest owes a lot to the broader revolution in understanding ovarian cancer origins. As evidence accumulated that many serous ovarian cancers start in the fallopian tube rather than the ovary itself, researchers began paying closer attention to any ectopic fallopian tube tissue, including endosalpingiosis. The discovery of shared BRAF and KRAS mutations between endosalpingiosis and low-grade serous tumors added molecular urgency to what had been a quiet histological observation. Improved tissue-sectioning protocols have also revealed that endosalpingiosis is far more prevalent than previously assumed, making it harder to dismiss as a negligible finding.16PubMed Central. Prevalence of endosalpingiosis and other benign gynecologic lesions
Still, prospective studies tracking women with endosalpingiosis over time to see who develops cancer and who does not have not been done. Without that kind of long-term data, the field cannot say with confidence whether endosalpingiosis is a genuine precursor, a bystander that shares a common cause with certain cancers, or something in between. The existing evidence is compelling enough to warrant serious investigation, but the studies that could definitively answer the question have yet to be designed and funded.