Should I Worry About Endometrial Cells on a Pap Smear?

For most women who are still having periods, benign-appearing endometrial cells on a Pap smear are a normal finding that does not signal disease. Endometrial cells routinely shed into the cervical canal during menstruation, and seeing them on a slide taken around that time is expected. The picture changes after menopause, when those same cells become a flag worth investigating because the uterine lining should be relatively quiet. Understanding where you fall on that spectrum, and whether the cells looked normal or atypical under the microscope, is what determines whether this result needs any follow-up at all.

Why Endometrial Cells Appear on a Pap Smear

The uterine lining sheds and regenerates every menstrual cycle, and fragments of that tissue can travel down through the cervix. A Pap smear collects cells from the cervix and the area around it, so it can inadvertently scoop up endometrial cells that have migrated from higher up. Research shows that the chance of picking up endometrial cells is highest during menstruation itself. After about day four of the cycle, through the proliferative phase, the percentage of smears containing endometrial cells drops sharply. During the secretory phase (roughly the second half of the cycle), only about 2% of smears contain them, and the rate rises again in the premenstrual days after day 25.¹

This means that the timing of your Pap test matters. If you happened to have a smear collected near the start or end of your period, the presence of endometrial cells is an expected artifact of timing, not a red flag. Your provider may note the cells on the report without recommending any follow-up at all.

The Reporting Threshold and Why Age Matters

Lab reports do not always mention endometrial cells. Under the Bethesda System, the standardized framework pathologists use to classify Pap smear findings, labs are currently instructed to report benign-appearing endometrial cells only in patients aged 45 and older.² This threshold was raised from 40 in 2014 after evidence accumulated that younger women almost never had significant pathology behind those cells.³

The logic is straightforward. In younger, premenopausal women, the uterine lining is supposed to be active, shedding regularly as part of normal cycles. When endometrial cells show up on a Pap in a 32-year-old, there is almost nothing to investigate. As women approach menopause and beyond, the lining thins and quiets down. Cells that should not be shedding anymore could hint at abnormal endometrial activity, including hyperplasia or, rarely, cancer. That is why the Bethesda guidelines draw a line: once you cross 45, the lab flags it so your clinician can decide whether further investigation is warranted.

Premenopausal Women and the Low Risk of Significant Findings

If you are premenopausal and your Pap report mentions benign endometrial cells, the odds of anything serious being behind them are very small. A study of women 40 and older found that among asymptomatic premenopausal women whose only abnormality was the presence of endometrial cells, roughly 2% had significant endometrial pathology, a rate that was essentially the same as in premenopausal women who had symptoms like abnormal bleeding.⁴ In other words, the cells themselves did not meaningfully predict trouble above and beyond what clinicians would already be watching for.

A large hospital-based review reinforced this, finding that women of any age with normal endometrial cells collected before day 12 of the menstrual cycle had a risk of significant endometrial disease of just 0.5%. Even after day 12, women younger than 50 with normal-appearing cells had only a 1.6% rate of significant findings. The researchers concluded that endometrial sampling provided no clinical benefit in either of those groups.⁵

Another review of clinical management echoed those conclusions: benign endometrial cells in premenopausal women during the first half of the cycle are not linked to significant disease, and these women do not need additional workup. Even in the second half of the cycle, significant findings are unlikely, and evaluation may not be needed unless something else is clinically concerning.⁶

After Menopause, the Calculus Changes

The story is quite different for postmenopausal women. Once menstruation has stopped, the uterine lining is not supposed to be actively shedding. When endometrial cells appear on a Pap smear in this setting, the chance that something clinically significant is going on rises substantially. One study found that among postmenopausal women whose cervical smears contained normal-appearing endometrial cells, the rate of precancerous or cancerous uterine disease was about 6.5%, compared to just 0.2% in postmenopausal women whose smears did not contain those cells. That translated to roughly a 40-fold higher relative risk.⁷

A study from Turkey looking at over 91,000 Pap smears found endometrial cells in just 0.1% of them. Among those cases that had complete follow-up, about 18% had premalignant or malignant findings, and menopausal status and being 50 or older were each significantly associated with those more serious diagnoses.⁸ A separate study looking specifically at postmenopausal women who had adequate biopsies after benign endometrial cells appeared on their Pap found that 18% had hyperplasia and another 18% had malignancy.⁹

These numbers do not mean that endometrial cells on a postmenopausal Pap smear are a cancer diagnosis. The majority of follow-up biopsies still come back benign. But the risk is high enough that virtually all guidelines recommend endometrial sampling when this finding appears after menopause, even if you have no symptoms at all.

Benign-Appearing Versus Atypical Endometrial Cells

Your Pap report will describe the endometrial cells as either benign-appearing (sometimes called “normal”) or atypical. This distinction matters far more than many patients realize. Atypical endometrial cells look abnormal under the microscope, and they carry a meaningfully higher risk of serious disease regardless of your age or menopausal status.

In the large hospital review mentioned earlier, the rate of significant endometrial lesions jumped from 2.7% in women with normal endometrial cells to 18.4% in women with atypical endometrial cells. Cases where the pathologist identified actual endometrial cancer cells on the smear had a 100% rate of confirmed malignancy on follow-up biopsy.⁵

Even within the atypical category, pathologists sometimes subdivide further. A recent study distinguished between atypical endometrial cells “not otherwise specified” (the more common, less alarming subtype) and atypical endometrial cells “favor neoplasia” (where the pathologist suspects a growth). Endometrial cancer was confirmed in about 10% of the “not otherwise specified” group but 27% of the “favor neoplasia” group.¹⁰ If your Pap report says “atypical endometrial cells,” an endometrial biopsy is standard practice, and your provider should explain what the specific wording means for your situation.⁶

What Follow-Up Looks Like

When follow-up is warranted, the most common next step is an endometrial biopsy, a brief in-office procedure where a thin tube is inserted through the cervix to collect a small tissue sample from the uterine lining. It is uncomfortable but usually quick. Transvaginal ultrasound is sometimes used as an alternative or a complement, measuring the thickness of the endometrial stripe; a thin lining in a postmenopausal woman is reassuring and can sometimes spare you a biopsy.

In practice, not every woman flagged with benign endometrial cells ends up getting biopsied. A study following the 2001 Bethesda guidelines (which used a lower age cutoff of 40) found that after the guidelines were implemented, the rate of endometrial biopsies went up significantly, and detection of endometrial cancer also increased modestly. All cancers detected were in women older than 45, which supported the later decision to raise the reporting threshold.¹¹

For asymptomatic women who are still premenopausal, the evidence suggests you can usually skip the biopsy. In one study that tracked 44 clinically asymptomatic women with normal endometrial cells for at least three years with only routine annual exams, all of them had negative clinical courses with no disease detected during follow-up.

Symptoms Change Everything

The biggest single factor that separates “don’t worry” from “get a biopsy” is whether you have symptoms, specifically abnormal vaginal bleeding. Irregular bleeding, bleeding between periods, unusually heavy periods, or any vaginal bleeding after menopause should always be evaluated, whether or not endometrial cells show up on a Pap smear.

Among postmenopausal women on hormone replacement therapy whose Pap smears showed normal endometrial cells, biopsies revealed abnormalities in about 19% of cases, including polyps, various forms of hyperplasia, and one case of endometrial cancer.¹² That 19% figure is striking, though it reflects a mixed group of symptomatic and asymptomatic women on HRT. The key takeaway is that HRT use adds a layer of complexity. These medications stimulate the endometrium, so shedding cells is more expected, but the stimulation itself can also promote abnormal changes that need monitoring.

How IUDs and Certain Medications Affect the Picture

Intrauterine devices can cause the uterine lining to shed cells more freely, which means IUD users are more likely to see endometrial cells on their Pap results. Research has found that copper IUD users in particular have a higher prevalence of bland endometrial cells on their Pap smears compared to users of other IUD types.¹³ Older studies found that IUD users could shed endometrial cells in any phase of the cycle, though earlier phases still showed the highest frequency, and the overall percentages were not dramatically different from non-users.¹⁴

Tamoxifen, a drug commonly used in breast cancer treatment, deserves special attention. It has estrogen-like effects on the uterine lining and is known to increase the risk of endometrial polyps, hyperplasia, and cancer. In a small study of postmenopausal women on tamoxifen whose smears contained endometrial cells, endometrial sampling revealed polyps in half of those biopsied.¹⁵ If you are taking tamoxifen and your Pap smear shows endometrial cells of any description, expect your provider to recommend prompt follow-up.

The Overdiagnosis Problem in Younger Women

One reason the Bethesda reporting age was raised from 40 to 45 is that the earlier threshold was generating biopsies with almost no yield. When the 2001 guidelines told labs to report benign endometrial cells in all women 40 and older, the result was a sharp increase in biopsies among premenopausal women, but virtually no pathology was found in those samples.¹⁶

A cost analysis underscored the point. Among over 1,000 women aged 40 and older shedding normal endometrial cells, about 350 asymptomatic women underwent endometrial sampling at an estimated total cost of over $107,000. Only three of those asymptomatic women had significant pathology, and all three were postmenopausal.¹⁷ The research community’s consensus has been clear: biopsying asymptomatic premenopausal women solely because of benign endometrial cells wastes resources and causes unnecessary anxiety and discomfort without meaningful health benefit.

If you are under 45, still menstruating regularly, have no abnormal bleeding, and your Pap report mentions endometrial cells in passing, the finding is genuinely unremarkable. Some labs will not even include it on the report at this age.

Liquid-Based Cytology Picks Up More Cells

Modern Pap smear technology has shifted from the traditional glass-slide method to liquid-based collection, where the sample is rinsed into a vial of preservative fluid. This technique is better at capturing cells and spreads them more evenly for the pathologist to read. One consequence is that liquid-based cytology detects atypical endometrial cells at a higher rate than conventional smears. In a large comparison of over 130,000 liquid-based samples and 409,000 conventional samples, the rate of atypical endometrial cell detection was about four times higher with liquid-based methods, while the rate of outright endometrial cancer detection was similar between the two.¹⁸

This means that if your Pap was processed using liquid-based cytology (most are in the United States and many other countries now), you may be more likely to see endometrial cells mentioned on your report than women were a generation ago. The technology is more sensitive, which is good for catching real problems but also means more incidental findings that turn out to be nothing. Knowing that your lab method can amplify these reports can help you put the result in context when you discuss it with your clinician.

A Practical Way to Think About Your Result

Rather than a blanket “worry or don’t worry,” the answer depends on a handful of specific factors about you. Here is how clinicians typically sort it out:

Premenopausal, no symptoms, first half of cycle: Benign endometrial cells are expected and virtually never linked to serious disease. No workup needed.
Premenopausal, no symptoms, second half of cycle: Still very low risk. Most experts say no biopsy is needed unless there is another clinical reason for concern.
Postmenopausal, no symptoms: The risk of a significant finding rises enough that endometrial sampling is generally recommended, even if the cells looked benign.
Any age, abnormal bleeding: A biopsy is warranted regardless of what the Pap shows. Abnormal bleeding is the single most important symptom for endometrial disease.
Atypical endometrial cells at any age: Endometrial sampling should be performed. The risk of serious pathology is substantially higher than with benign-appearing cells.
On tamoxifen or HRT: These medications stimulate the uterine lining, making endometrial cells more likely to appear and also raising the baseline risk of endometrial changes. Your provider will likely recommend follow-up even if the cells appear benign.

If you are still menstruating and had your Pap taken around the time of your period, a note about endometrial cells on the report is genuinely routine. In that scenario the finding tells your doctor more about your cycle timing than about your uterine health. Providers who see these results regularly know that most of them lead nowhere, and when they do recommend follow-up, the endometrial biopsy itself is a quick, low-risk procedure designed to put your mind at ease or catch a treatable problem early.