Endometrial Polyps: Causes, Cancer Risk, and Removal

Endometrial polyps are soft, finger-like growths of the uterine lining that project into the uterine cavity. They are among the most common findings on pelvic ultrasound, turning up in roughly a quarter of women with abnormal uterine bleeding, and they range from a few millimeters to several centimeters across. Most are benign, but the picture is more layered than “harmless growths you can ignore,” especially when it comes to fertility, cancer risk, and whether removal actually helps.

Why They Form

Endometrial polyps grow from the same tissue that lines the uterus and sheds during menstruation, but they don’t behave quite the same way. The glandular cells inside a polyp carry higher concentrations of both estrogen and progesterone receptors than the normal surrounding endometrium, while the stroma (the supportive tissue underneath) looks about the same as normal lining.¹ That receptor imbalance means the glands inside a polyp respond to estrogen more aggressively, growing faster while resisting the normal shedding signals that progesterone provides.

There’s also a molecular angle. Polyps from both premenopausal and postmenopausal women show elevated levels of Bcl-2, a protein that blocks programmed cell death.² In plain terms, the cells that make up a polyp are better at surviving than their neighbors, so they accumulate while the rest of the lining turns over normally. Genetic rearrangements have also been found in some polyps, particularly involving genes that overlap with those seen in other common benign tumors like uterine fibroids and lipomas.³

Who Is Most at Risk

Some factors consistently show up in the research. Higher body weight is one. Women with endometrial polyps tend to have a significantly higher BMI than women without them, which fits the hormonal story: fat tissue produces estrogen, and more circulating estrogen feeds the receptor-rich glandular cells inside a polyp.⁴ That same study found no significant link with diabetes or high blood pressure on their own, though obesity often travels with both conditions, which may be why the association feels intuitive to many clinicians.

Tamoxifen, a drug widely used in breast cancer treatment, is a well-known risk factor. Tamoxifen acts as an estrogen blocker in breast tissue but has estrogen-like effects on the uterus, and women taking it develop endometrial polyps at notably high rates. In one retrospective analysis of over 800 biopsies from tamoxifen-treated women, polyps were found in about one in five, and the risk rose with longer duration of use and greater endometrial thickness.⁵ Age and menopausal status also matter: polyps become more common as women approach menopause, likely because of the hormonal fluctuations that characterize that transition.

Symptoms and When to Worry

The textbook symptom is abnormal uterine bleeding: heavier periods, bleeding between periods, or unexpected bleeding after menopause. But plenty of endometrial polyps produce no symptoms at all and get discovered incidentally during an ultrasound for something else entirely. This creates a genuine dilemma for both patients and doctors, because asymptomatic polyps are common and the question of what to do with them isn’t simple.

When symptoms do occur, the type of bleeding often depends on the polyp’s anatomy. Pedunculated polyps, the kind that dangle on a stalk into the uterine cavity, are more closely linked to abnormal bleeding than sessile (broad-based) ones.⁶ This makes mechanical sense: a polyp swinging freely on a stalk is more likely to irritate the surrounding tissue and bleed.

Can They Go Away on Their Own

Yes, sometimes. The spontaneous regression question is one of the most practically important, because it determines whether a “wait and watch” approach is reasonable. The numbers vary by study and by how long researchers waited. One study found that about a quarter of small polyps resolved on their own within a year.⁷ A longer-term study tracking women for a median of about two and a half years found a lower regression rate, closer to 6%.⁸

The best predictors of spontaneous regression are younger age, premenopausal status, and smaller polyp size (under about 2 cm).⁹ So for a younger woman with a small, asymptomatic polyp and no concerning risk factors, it’s reasonable to recheck in several months before jumping to surgery. For postmenopausal women with larger polyps, regression is much less likely and the calculus shifts toward removal.

How They Are Diagnosed

The first clue usually comes from a standard transvaginal ultrasound, which can pick up a thickened or irregular endometrium. But standard ultrasound alone has real limitations for confirming polyps. Its sensitivity for detecting endometrial polyps is only about 55%, meaning it misses nearly half of them, though its specificity is higher at around 91%, so when it does spot something that looks like a polyp, it’s usually right.¹⁰

Saline infusion sonohysterography, where sterile saline is injected into the uterine cavity to expand it during the ultrasound, dramatically improves the picture. Sensitivity jumps to about 87–92% and specificity stays high at 86–93%, depending on the meta-analysis.¹¹ Hysteroscopy, where a thin camera is passed through the cervix to look directly inside the uterus, has the highest sensitivity at about 92%, and it also allows biopsy or removal in the same session.

One important caveat: office-based biopsies done through a hysteroscope have surprisingly low sensitivity for diagnosing what a polyp actually is. Compared to specimens from full surgical removal, hysteroscopically guided biopsies of the apex and base of the polyp had sensitivities of only about 35–37%.¹² This is why most specialists prefer to remove the whole polyp rather than just biopsy it: piecemeal sampling can miss areas of concern.

Telling Polyps from Fibroids on Imaging

Endometrial polyps and submucosal fibroids can look frustratingly similar on a basic ultrasound, which is why they’re often confused. But there are reliable ways to distinguish them. On sonohysterography, polyps tend to appear as homogeneous, uniformly bright (hyperechoic) masses, while fibroids are more varied in their echogenicity and tend to be larger. Masses over 20 mm are significantly more likely to be fibroids.¹³

Color Doppler imaging adds another layer. Polyps typically have a single feeding blood vessel running up through the stalk, whereas fibroids tend to have multiple vessels arising from the surrounding muscle wall.¹⁴ Newer techniques like elastography can also help, since polyps are soft and compressible while fibroids are firm and rigid.¹⁵ The distinction matters because the surgical approach, long-term management, and clinical implications differ between the two.

Malignancy Risk

This is the question that often drives the decision to remove a polyp, and the honest answer is that while most endometrial polyps are benign, a small but meaningful fraction harbors premalignant or malignant changes. In a South Korean study of 725 patients, about 7% of polyps showed premalignant or malignant features on pathology.¹⁶ The risk was not spread evenly. Menopause carried the strongest association, with about eight times the odds. Abnormal bleeding, obesity, having multiple polyps, and never having given birth all independently raised the risk as well.

Larger polyps carry more concern. One study found that polyps 2.25 cm or longer had over thirteen times the odds of being malignant compared to smaller ones. Higher fasting blood glucose and elevated inflammatory markers also predicted malignancy.¹⁷ The most frequently studied risk factors in the literature overall are age, postmenopausal bleeding, and polyp size.¹⁸

For tamoxifen users, the malignancy picture is slightly different. In one series of 67 polyps removed from postmenopausal breast cancer patients on tamoxifen, two (about 3%) turned out to be malignant.¹⁹ This is why tamoxifen users who develop polyps are generally recommended for removal rather than observation.

At the molecular level, a useful distinction between benign polyps and those harboring cancer involves a protein called Ki-67, a marker of cell proliferation. Cancerous polyps show significantly higher Ki-67 levels, while paradoxically their Bcl-2 expression (the anti-cell-death protein that’s elevated in benign polyps) actually drops.²⁰ Researchers are exploring whether these markers could eventually help triage which polyps need urgent removal, though for now the standard practice is still to send all removed polyps for pathological analysis.

Treatment and Surgical Options

Hysteroscopic polypectomy, where a camera is placed inside the uterus and the polyp is removed under direct vision, is the gold standard. It consistently outperforms blind curettage (D&C), where the uterine lining is scraped without visual guidance. In one comparison, the recurrence rate after D&C was about 27%, versus under 2% after hysteroscopic removal.²¹ The reason is straightforward: if you can see the polyp’s base and remove it completely, there’s less tissue left behind to regrow.

Within hysteroscopy, there are two main approaches: traditional bipolar resectoscopy (using an electrified loop to slice the polyp) and newer mechanical tissue removal systems (sometimes called hysteroscopic morcellators, which use a small rotating blade with suction). A meta-analysis found that the tissue removal systems cut operating time by about three minutes on average compared to resectoscopy.²² A randomized trial put it more concretely: median operating time was 4 minutes with the morcellator versus 6 minutes with the resectoscope, a 38% reduction.²³

Despite the speed advantage, long-term outcomes appear similar between the two techniques. One study with follow-up averaging over eight years found no significant difference in polyp recurrence, symptom relief, or return of abnormal bleeding between tissue removal systems and bipolar resection.²⁴ So the choice between methods often comes down to surgeon preference, equipment availability, and whether the procedure is being done in-office (where tissue removal systems tend to shine because they’re faster and can be used with smaller instruments) or in an operating room.

Polyps and Fertility

Endometrial polyps are found in a significant fraction of women being evaluated for infertility, and the question of whether they actually interfere with conception is one of the more debated areas in reproductive medicine. The proposed mechanisms include physical obstruction of sperm or embryo transport, disruption of the uterine environment through local inflammation, and altered production of factors that help the lining accept an embryo.²⁵

The evidence for removing polyps before fertility treatment is clearest for intrauterine insemination (IUI). A systematic review found that hysteroscopic removal of polyps under 2 cm improved clinical pregnancy rates for IUI patients. But for women undergoing IVF, the picture was murkier: the review found no clear benefit in pregnancy, live birth, miscarriage, or implantation rates after removal.²⁶ This may be because IVF bypasses some of the mechanical obstacles a polyp creates, or because the studies were simply too small to detect a real difference.

One retrospective study compared pregnancy outcomes specifically by surgical technique. Women who had polyps removed hysteroscopically before embryo transfer had a pregnancy rate of about 68% on the first transfer, compared to about 51% in women who had curettage-based removal. Live birth rates followed a similar pattern: roughly 66% versus 53%.²⁷ That suggests the completeness of removal matters for fertility outcomes, not just whether the polyp is gone but how thoroughly it was taken out.

Recurrence and How to Prevent It

Polyps come back more often than you might expect. Recurrence rates in the literature range widely depending on follow-up time and study design. One study reported recurrence in about 43% of women, though over a long follow-up period, and found that having multiple polyps at baseline and longer follow-up were the strongest predictors.²⁸ Other, larger studies have found lower rates closer to 8%, with a median time to recurrence of about three and a half years.²⁹ Higher BMI, elevated estrogen levels, greater endometrial thickness, and larger polyps all increase recurrence risk.³⁰

Conditions that coexist with polyps, particularly adenomyosis and polycystic ovarian syndrome (PCOS), also carry substantial recurrence risk. In one analysis, women with adenomyosis had about ten times the odds of recurrence, and those with PCOS had about nine times the odds.³¹

The most studied prevention strategy is the levonorgestrel-releasing intrauterine system (known by brand names like Mirena). This is a hormonal IUD that delivers a small, steady dose of a progesterone-like hormone directly to the uterine lining. Multiple studies confirm it substantially reduces recurrence. In one retrospective cohort, only about 3.5% of women with the device experienced recurrence within three years, compared to about 16% without it.³² Other hormonal options like combined oral contraceptives and progestins have also shown lower recurrence rates compared to no treatment, though the hormonal IUD consistently performs best.³³

Premenopausal Versus Postmenopausal Polyps

Polyps in premenopausal and postmenopausal women share some biological features but differ in others that affect clinical management. Both types show elevated Bcl-2, the anti-apoptosis protein mentioned earlier, but their hormone receptor profiles and cell proliferation markers differ significantly.³⁴ Premenopausal polyps are more hormonally active and more likely to regress on their own, which makes watchful waiting a more reasonable strategy in this group.

Interestingly, the actual rate of malignancy when stratified strictly by menopausal status may not be as different as the risk-factor studies suggest. One study looking at confirmed pathology found malignancy in about 2% of both premenopausal and postmenopausal women.³⁵ The difference is that postmenopausal women are far more likely to have other co-existing risk factors like obesity, abnormal bleeding, and larger or multiple polyps, which collectively drive the higher malignancy rates seen in broader analyses. This is why age alone doesn’t determine the need for removal: the whole risk profile matters.