National Cancer Institute


Expert-reviewed information summary about factors that may influence the risk of developing endometrial cancer and about research aimed at the prevention of this disease.

This PDQ cancer information summary for health professionals provides comprehensive, peer-reviewed, evidence-based information about endometrial cancer prevention. It is intended as a resource to inform and assist clinicians who care for cancer patients. It does not provide formal guidelines or recommendations for making health care decisions.

This summary is reviewed regularly and updated as necessary by the PDQ Screening and Prevention Editorial Board, which is editorially independent of the National Cancer Institute (NCI). The summary reflects an independent review of the literature and does not represent a policy statement of NCI or the National Institutes of Health (NIH).

Endometrial Cancer Prevention

Who Is at Risk?

Endometrial cancer occurs in postmenopausal women with an average age at diagnosis of 60 years. Estrogen, both endogenous and exogenous, is associated with endometrial proliferation, hyperplasia, and cancer. Thus, risk factors include endometrial hyperplasia, reproductive factors (nulliparity, early menarche and late menopause), polycystic ovarian syndrome, postmenopausal estrogen therapy, obesity with adult weight gain, and tamoxifen use. Women with hereditary nonpolyposis colorectal cancer syndrome have an increased risk of endometrial cancer, as do women with a first-degree relative with endometrial cancer.

Overview

Note: Separate PDQ summaries on Endometrial Cancer Screening; Endometrial Cancer Treatment; and Uterine Sarcoma Treatment are also available.

Factors with Adequate Evidence for an Increased Risk of Endometrial Cancer

Endometrial hyperplasia

Based on solid evidence, endometrial hyperplasia is associated with concurrent or subsequent development of cancer, an association first recognized in 1932.

Magnitude of Effect: Women with hyperplasia and atypia have a 50% risk of concurrent cancer.

  • Study Design: Observational case series.
  • Internal Validity: Good.
  • Consistency: Good.
  • External Validity: Good.

Hormone therapy (HT) with estrogen: Unopposed estrogen

Based on solid evidence, unopposed estrogen is associated with an increased risk of endometrial cancer. This excess risk can be eliminated by adding continuous progestin to estrogen therapy, but this combination is associated with an increased risk of breast cancer. (Refer to the PDQ summary on Breast Cancer Prevention for more information.)

Magnitude of Effect: The associated risk of endometrial cancer in women using unopposed estrogen for 5 or more years is more than twofold higher than in women who do not use the hormone.

  • Study Design: Randomized controlled trials, cohort, and case-control studies.
  • Internal Validity: Good.
  • Consistency: Good.
  • External Validity: Good.

Based on solid evidence, in addition to the risk of endometrial cancer, unopposed estrogen is associated with an increased risk of endometrial hyperplasia, stroke, and thrombosis.

Magnitude of Effect: Unopposed estrogen after a mean follow-up of 6.8 years: Approximately a 39% relative increase in stroke and a 34% relative increase in pulmonary embolus.

  • Study Design: Randomized placebo-controlled trials.
  • Internal Validity: Good.
  • Consistency: Good.
  • External Validity: Good.

Selective estrogen receptor modifiers (SERMs)

Based on solid evidence, more than 2 years of tamoxifen use is associated with an increased risk of endometrial cancer. A similar SERM, raloxifene, does not have this association.

Magnitude of Effect: Women taking tamoxifen for more than 2 years have a 2.3-fold to 7.5-fold relative risk (RR) of endometrial cancer.

  • Study Design: Multiple randomized controlled trials.
  • Internal Validity: Good.
  • Consistency: Good.
  • External Validity: Good.

Obesity and diabetes

Based on solid evidence, being overweight or obese, adult weight gain, and diabetes are associated with an increased risk of endometrial cancer.

Magnitude of Effect: The risk of endometrial cancer increases 1.59-fold per 5 kg/m change in body mass.

  • Study Design: Multiple randomized controlled trials.
  • Internal Validity: Good.
  • Consistency: Good.
  • External Validity: Good.

Factors With Adequate Evidence for a Decreased Risk of Endometrial Cancer

Increasing parity and lactation

Based on solid evidence, increased parity and duration of lactation are associated with a decreased risk of endometrial cancer.

Magnitude of Effect: Parous women have a 35% decreased risk of endometrial cancer (hazard ratio, 0.65; 95% confidence interval [CI], 0.54–0.77) compared with nulliparous women. Duration of breastfeeding has also been associated with a decreased risk, with a 23% risk reduction noted with breastfeeding more than 18 months. The risk reduction was attenuated when adjusted for parity.

  • Study Design: Prospective cohort study.
  • Internal Validity: Good.
  • Consistency: Good.
  • External Validity: Good.

Oral contraceptives

Benefits

Based on solid evidence, at least 1-year use of oral contraceptives containing estrogen and progesterone decreases endometrial cancer risk, proportionate to duration of use. This benefit lasts at least 15 years after cessation.

  • Study Design: Case-control studies and prospective studies.
  • Internal Validity: Good.
  • Consistency: Good.
  • External Validity: Good.

Magnitude of Effect: Use of oral contraceptives for 5 years was associated with an RR reduction of 24% (risk ratio, 0.76; 95% CI, 0.73–0.78) and persisted for more than 30 years. Ten years of use was associated with an absolute reduction in risk before age 75 years from 2.3 per 100 women to 1.3 per 100 women.

Harms

Based on solid evidence, current use of oral contraceptives is associated with an increased risk of blood clots, stroke, and myocardial infarction, especially among women who smoke cigarettes and who are older than 35 years.

  • Study Design: Randomized controlled clinical trials.
  • Internal Validity: Good.
  • Consistency: Good.
  • External Validity: Good.

Physical activity

Based on solid evidence, increased physical exercise is associated with a decreased risk of endometrial cancer.

Magnitude of Effect: Regular exercise may be associated with a 38% to 46% decrease in risk, although a trend in risk reduction with increasing duration or intensity has not been shown.

  • Study Design: Multiple cohort and case-control studies.
  • Internal Validity: Good.
  • Consistency: Fair.
  • External Validity: Good.

Smoking

Benefits

Based on solid evidence, cigarette smoking is associated with a decreased risk of endometrial cancer.

Magnitude of Effect: Smokers have a reduced risk of endometrial cancer of approximately 20% among prospective studies (RR, 0.81; 95% CI, 0.74–0.88) and case-control studies (odds ratio, 0.72; 95% CI, 0.66–0.79).

  • Study Design: Prospective cohort and case-control studies.
  • Internal Validity: Good.
  • Consistency: Good.
  • External Validity: Good.

Harms

Based on solid evidence, cigarette smoking is associated with cardiovascular disease and cancers of the head and neck, lung, bladder, and pancreas. Cigarette smokers have a decreased life expectancy—they live at least 10 years fewer than nonsmokers.

Intervention With Inadequate Evidence of an Association With Endometrial Cancer

Weight loss

The evidence is insufficient to conclude whether weight loss is associated with a decreased incidence of endometrial cancer. Based on one study, self-reported intentional weight loss during three age periods was not associated with a decrease in endometrial cancer incidence.

Magnitude of Effects: RR of endometrial cancer for women who intentionally lost at least 20 pounds was 0.93 (95% CI, 0.6–1.44).

  • Study Design: Cohort study with retrospectively self-reported data.
  • Internal Validity: Good.
  • Consistency: Good.
  • External Validity: Good.

Description of Evidence

Background

Incidence and mortality

Endometrial cancer is the most common invasive gynecologic cancer in U.S. women, with an estimated 61,380 new cases expected to occur in 2017. This disease primarily affects postmenopausal women at an average age of 60 years at diagnosis. In the United States, it is estimated that approximately 10,920 women will die of endometrial cancer in 2017. From 2004 to 2013, incidence rates of endometrial cancer have increased by 1% per year in white women and by 3% per year in African American women. From 2005 to 2014, death rates for endometrial cancer increased by about 1% per year in white women and by 2% per year in African American women.

Compared with white Americans, endometrial cancer incidence is lower in Japanese Americans (relative risk [RR], 0.6; 95% confidence interval [CI], 0.46–0.83) and in Latinas (RR, 0.63; 95% CI, 0.46–0.87), but not in African Americans (RR, 0.76; 95% CI, 0.53–1.08) or in native Hawaiians (RR, 0.92; 95% CI, 0.58–1.46). Higher mortality from endometrial cancer in African Americans is at least partly attributable to lower socioeconomic issues that impair access to care.

Endometrial cancer risk is associated with endogenous and exogenous factors associated with estrogen effects. Thus, risk factors for endometrial cancer include reproductive factors such as nulliparity, early menarche, and late menopause, obesity, polycystic ovarian syndrome, postmenopausal estrogen use and tamoxifen use.

Women with hereditary nonpolyposis colorectal cancer syndrome have a lifetime risk of endometrial cancer of up to 60%. (Refer to the PDQ summary on Genetics of Breast and Gynecologic Cancers for additional information on inherited risk.)

Factors With Adequate Evidence for an Increased Risk of Endometrial Cancer

Endogenous estrogen

Reproductive factors resulting in increased duration of exposure to endogenous estrogen, such as early menarche, nulliparity, and late menopause, are associated with an increased risk of endometrial cancer. Other factors associated with increased risk, such as obesity and polycystic ovarian syndrome, may also be related to increased estrogen exposure.

Postmenopausal estrogen therapy

An association between postmenopausal estrogen replacement therapy and endometrial cancer was reported in 1975 and confirmed soon after. In these three studies, the overall risk ratio ranged from 4.5 to 8.0. Further studies documented an association with duration of use (10-fold to 30-fold with 5 years or more of use), and a persistent effect lasting more than 10 years after 1 year of use. When these findings were publicized, prescriptions for estrogen declined sharply, followed rapidly by a drop in endometrial cancer incidence.

Combination estrogen-progestin replacement therapy

Postmenopausal estrogen was long recognized to be associated with the risk of endometrial hyperplasia, often a precursor of endometrial cancer. In addition, progestational agents were known to be effective in the treatment of uterine neoplasms. Consequently, combined estrogen-progesterone postmenopausal hormone therapy (HT) was proposed to avoid the endometrial cancer risk associated with unopposed estrogen. Unfortunately, the combined therapy increases the risk of breast cancer, so it is not recommended to treat menopausal symptoms.

Selective estrogen receptor modulators (SERMs): Tamoxifen and raloxifene

Tamoxifen and raloxifene are SERMs, drugs that have divergent estrogen agonist and antagonist effects in different target organs. The association between endometrial cancer and tamoxifen was first recognized in 1985 when three cases of endometrial cancer were described in women who had been treated with tamoxifen for breast cancer. Since then, confirmation of the association has been provided by randomized clinical trials using tamoxifen for breast cancer treatment and prevention and by case-control, observational, and laboratory studies.

The National Surgical Adjuvant Breast and Bowel Project, Breast Cancer Prevention Trial P-1 Study in women at high risk of invasive breast cancer demonstrated that tamoxifen decreased breast cancer incidence by 49%, but confirmed an increased incidence of endometrial cancer. The annual rate was 2.3 cases per 1,000 women for those receiving tamoxifen versus 0.91 cases per 1,000 women for those on placebo. Women older than 50 years experienced the largest effect. Of the 51 invasive cancers diagnosed in this trial, 50 were stage I.

Raloxifene is a second-generation SERM approved for prophylaxis against postmenopausal osteoporosis. Unlike tamoxifen, it does not have an estrogenic effect on the uterus. The Multiple Outcomes of Raloxifene randomized trial, after 40 months of follow-up, showed that raloxifene reduced the risk of estrogen receptor–positive breast cancer, without increasing endometrial cancer (RR, 0.8; 95% CI, 0.2–2.7). A population-based study of 547 women with endometrial cancer and 1,410 controls was done in Philadelphia, Pennsylvania. Of the cases, 18 (3.3%) had taken raloxifene and 34 (6.2%) had taken tamoxifen (odds ratio [OR], 3.0; 95% CI, 1.3–6.9).

Obesity, weight gain, metabolic syndrome, and diabetes

Elevated body mass index (BMI), obesity, and weight gain are associated with an increased risk of endometrial cancer. One of the possible mechanisms for the observed association is an increased level of serum estrone in obese women as a result of aromatization of androstenedione in adipose tissue, which increases the production of estrogen. Alternatively, obesity has been associated with a reduction in levels of sex hormone-binding globulin (SHBG), which may protect against endometrial cancer by decreasing bioavailable estrogen. Obesity has been associated with several factors known to increase the risk of endometrial cancer, including upper-body or central adiposity, polycystic ovarian syndrome, and physical inactivity.

Body weight is a modifiable risk factor, which accounts for a substantial proportion of endometrial cases worldwide. A study conducted among European countries estimated that between 26% and 47% of endometrial cancer cases can be attributed to overweight and obesity. The same group conducted a meta-analysis of 12 studies (5 cohort and 7 case-control), which examined the relationship between obesity and endometrial cancer. Eleven of the 12 studies concluded that there is a positive association between endometrial cancer and excess weight.

RRs associated with obesity range from 2 to 10. Some studies show that upper-body and central weight confer a higher risk than peripheral body weight, even after consideration of BMI. However, other studies have failed to confirm such an association. Several studies have observed a stronger association between endometrial cancer and obesity near the time of diagnosis compared with obesity earlier in life. An increased risk is observed across all measures of adiposity, such as BMI, waist circumference, waist-to-hip ratio, and weight gain.

A meta-analysis of prospective studies observed an RR of 1.39 (95% CI, 1.29–1.49) among nonusers and 1.09 (95% CI, 1.02–1.16) among HT users for each 5 kg increase in adult weight gain. Another meta-analysis also observed a stronger association between BMI and the risk of endometrial cancer in never-users of HT than in ever-users of HT.

A meta-analysis examining the association between metabolic syndrome and endometrial cancer observed an increased risk associated with metabolic syndrome (RR, 1.89; 95% CI, 1.34–2.67) and with each component of the syndrome (BMI and/or waist circumference, blood pressure, and triglyceride levels), except low high-density lipoprotein cholesterol. In an umbrella analysis of studies of the association between type 1 diabetes and cancer, endometrial cancer was one of only a few sites with robust evidence of an association.

Genetic predisposition

Women with inherited conditions such as Lynch syndrome, Cowden syndrome, and polycystic ovarian syndrome have an increased risk of endometrial cancer. (Refer to the PDQ summaries on Genetics of Breast and Gynecologic Cancers and Genetics of Colorectal Cancer for more information.) However, in addition to inherited syndromes with highly penetrant genes, having a family history of endometrial cancer in a first-degree relative also is associated with an increased risk of cancer. A meta-analysis, including case-control and cohort studies, observed an increased risk of 1.82 (95% CI, 1.65–1.98) associated with a history of endometrial cancer in a first-degree relative, with an estimated cumulative absolute risk of about 3% (95% CI, 2.8–3.4).

This familial risk may result from inherited genetic predisposition and other common factors that exist is families, such as shared culture or learned behaviors.

Factors With Adequate Evidence for a Decreased Risk of Endometrial Cancer

Increasing parity and lactation

Decreased risk of endometrial cancer is associated with parity and lactation, perhaps by inhibiting ovulation. A case-control study conducted in Mexico City, among low-risk women, indicates a 58% to 72% reduction in risk of endometrial cancer associated with increasing duration of lactation. A significant trend was seen for duration of lactation and for the number of children breastfed. A population-based case-control study, comparing Wisconsin women who breastfed for at least 2 weeks versus those who did not, was negative (OR, 0.90; 95% CI, 0.72–1.13). Increasing duration of lactation was not associated with a decrease in disease risk, but breastfeeding within the past three decades was associated with reduced risk (OR, 0.58; 95% CI, 0.36–0.96), as was the first breastfeeding after age 30 years (95% CI, 0.28–0.90). The European Prospective Investigation into Cancer and Nutrition observed a decreased risk associated with parity compared with nulliparous women (hazard ratio, 0.65; 95% CI, 0.54–0.77) with a trend of decreasing risk with increasing number of full-term pregnancies ( < .0001). While breastfeeding for more than 18 months was associated with a decreased risk, the association attenuated and was no longer statistically significant after adjusting for the numbers of full-term pregnancies.

Oral contraceptives

Oral contraceptive usage confers a long-term reduction in the risk of endometrial cancer. A meta-analysis combining data from 36 epidemiological studies including 27,276 women observed a risk reduction of 0.76 (95% CI, 0.73–0.78) for every 5 years of use. The lower risk persisted for more than 30 years after the last use of oral contraceptives. Ten years of oral contraceptive use was associated with an absolute risk reduction of endometrial cancer before age 75 from 2.3 to 1.3 per 100 women, among women from highly developed countries.

Physical activity

A meta-analysis combined data from prospective studies of recreational activity (nine studies) and occupational activity (five studies) to determine whether activity is association with endometrial cancer. The highest versus the lowest category of recreational activity was associated with an RR for endometrial cancer of 0.73 (95% CI, 0.58–0.93); the RR of endometrial cancer for the highest versus lowest category of occupational physical activity, based on job classification, was 0.75 (95% CI, 0.68–0.83.) Further investigation using the metabolic equivalent of task (MET) and combining data from case-control and cohort studies, revealed a decrease in endometrial cancer risk with activities in the range up to 50 MET hours per week (up to 15 hours/week).

Smoking

Ever-smokers of at least 20 cigarettes per day have a decreased risk of endometrial cancer, with greater risk reduction in postmenopausal women and in current smokers. This effect has been seen in prospective cohort and case-control studies and was summarized in a meta-analysis. The many well-documented harms of smoking are most evident in the increased risk of cardiovascular diseases and other cancers, to the extent that smokers have at least a 10-year decrease in life expectancy, compared with nonsmokers.

Interventions With Inadequate Evidence of an Association With Endometrial Cancer

Weight loss

While it is known that obesity is associated with increased endometrial cancer risk, only one study examines the potential benefit of intentional weight loss. In the Iowa Women’s Health Study (IWHS) of 21,707 postmenopausal women, participants completed a self-report questionnaire about intentional weight loss between ages 18 and 39 years, between ages 40 and 54 years, and after age 55 years. Multivariate models adjusting for age, BMI, and BMI found no association between endometrial cancer incidence and intentional weight loss of at least 20 pounds (RR, 0.93; 95% CI, 0.60–1.44). However, an analysis of 36,793 women from the Women’s Health Initiative (WHI) cohort whose weight measured at baseline and 3-year follow-up was combined with self-reported intentionality of weight loss showed an association between intentional weight loss of 10 pounds or more and lower endometrial cancer incidence (multivariable-adjusted RR, 0.61; 95% CI, 0.40–0.92).

Both of these analyses share substantial limitations. Missing covariate data resulted in excluding nearly 25% of participants from each study, and only small percentages of the remaining participants (17% IWHS / 8% WHI) were classified into the category, resulting in very low numbers of endometrial cancer cases driving the analyses. Both studies used self-report to characterize intentionality of weight loss, which can lead to potential misclassification, although the retrospective nature of the questioning in the IWHS makes the problem more acute in that analysis. Both analyses also adjusted for self-reported (and thus prone to measurement error) physical activity and smoking status, among other covariates. With such small numbers of cases and the potential for residual confounding, the contradictory results of these two analyses suggest that there is scant evidence to conclude that weight loss is protective for endometrial cancer.

Fruits, vegetables, and vitamins

Studies of the association between endometrial cancer and diet, phytoestrogens, soy, and vitamin D have been negative. Multivitamin use has little or no influence on the risk of common cancers, including endometrial cancer, or on total mortality in postmenopausal women.

Changes to This Summary (07/27/2017)

The PDQ cancer information summaries are reviewed regularly and updated as new information becomes available. This section describes the latest changes made to this summary as of the date above.

Description of Evidence

Added text about an analysis of 36,793 women from the Women's Health Initiative cohort whose weight was measured at baseline and 3-year follow-up and was combined with self-reported intentionally of weight loss that showed an association between intentional weight loss of 10 pounds or more and lower endometrial cancer incidence (cited Luo et al. as reference 58).

Added text to state that both of these analyses share substantial limitations; with such small numbers of cases and the potential for residual confounding, the contradictory results of these two analyses suggest that there is scant evidence to conclude that weight loss is protective for endometrial cancer.

This summary is written and maintained by the PDQ Screening and Prevention Editorial Board, which is editorially independent of NCI. The summary reflects an independent review of the literature and does not represent a policy statement of NCI or NIH. More information about summary policies and the role of the PDQ Editorial Boards in maintaining the PDQ summaries can be found on the About This PDQ Summary and PDQ® - NCI's Comprehensive Cancer Database pages.

About This PDQ Summary

Purpose of This Summary

This PDQ cancer information summary for health professionals provides comprehensive, peer-reviewed, evidence-based information about endometrial cancer prevention. It is intended as a resource to inform and assist clinicians who care for cancer patients. It does not provide formal guidelines or recommendations for making health care decisions.

Reviewers and Updates

This summary is reviewed regularly and updated as necessary by the PDQ Screening and Prevention Editorial Board, which is editorially independent of the National Cancer Institute (NCI). The summary reflects an independent review of the literature and does not represent a policy statement of NCI or the National Institutes of Health (NIH).

Board members review recently published articles each month to determine whether an article should:

  • be discussed at a meeting,
  • be cited with text, or
  • replace or update an existing article that is already cited.

Changes to the summaries are made through a consensus process in which Board members evaluate the strength of the evidence in the published articles and determine how the article should be included in the summary.

Any comments or questions about the summary content should be submitted to Cancer.gov through the NCI website's Email Us. Do not contact the individual Board Members with questions or comments about the summaries. Board members will not respond to individual inquiries.

Levels of Evidence

Some of the reference citations in this summary are accompanied by a level-of-evidence designation. These designations are intended to help readers assess the strength of the evidence supporting the use of specific interventions or approaches. The PDQ Screening and Prevention Editorial Board uses a formal evidence ranking system in developing its level-of-evidence designations.

Permission to Use This Summary

PDQ is a registered trademark. Although the content of PDQ documents can be used freely as text, it cannot be identified as an NCI PDQ cancer information summary unless it is presented in its entirety and is regularly updated. However, an author would be permitted to write a sentence such as “NCI’s PDQ cancer information summary about breast cancer prevention states the risks succinctly: [include excerpt from the summary].”

The preferred citation for this PDQ summary is:

PDQ® Screening and Prevention Editorial Board. PDQ Endometrial Cancer Prevention. Bethesda, MD: National Cancer Institute. Updated . Available at: https://www.cancer.gov/types/uterine/hp/endometrial-prevention-pdq. Accessed . [PMID: 26389477]

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