Endometrial cancer is the fourth most common cancer in women in the developed world, with incidence doubling over the past 20 years. A major driver of this increase is rising obesity rates. Obesity promotes endometrial cancer through three biological mechanisms: unopposed oestrogen (fat tissue converts testosterone to oestrogen, stimulating endometrial cell growth), insulin resistance (elevated insulin activates cancer-promoting pathways), and chronic inflammation (fat tissue produces inflammatory proteins that encourage tumor development).
Beyond causing cancer, obesity also complicates treatment and worsens outcomes. Obese women face higher surgical complication rates, more complex radiotherapy planning, and are twice as likely to die during the follow-up period as healthy-weight women. Women with a BMI of 30 or more are twice as likely to die as those at a healthy weight, and this risk increases sixfold when BMI exceeds 40. Cardiovascular disease is a frequent cause of death in endometrial cancer survivors, and obesity is a major risk factor for both conditions.
This Cochrane systematic review asked whether weight-loss interventions, added to standard endometrial cancer management, could improve overall survival, reduce adverse events, and enhance quality of life. Weight-loss strategies considered included lifestyle changes (diet and exercise), pharmacological treatments, and bariatric surgery.
The review followed rigorous Cochrane methodology, searching multiple databases including CENTRAL, MEDLINE, and Embase from inception to January 2018, with no language restrictions. Trial registries and conference proceedings were also searched. The review included only randomised controlled trials (RCTs) comparing weight-loss interventions to usual care, placebo, or other interventions in overweight or obese women (BMI over 25 or 30) undergoing or having completed treatment for endometrial cancer.
Two review authors independently screened studies, extracted data, and assessed risk of bias. The quality of evidence was evaluated using the GRADE framework, which rates confidence in findings from very low to high based on study limitations, consistency, precision, and directness of evidence. Primary outcomes were overall survival and adverse event frequency. Secondary outcomes included cancer-specific survival, recurrence-free survival, weight loss, cardiovascular events, and quality of life.
Data were pooled using meta-analysis where appropriate, with risk ratios for dichotomous outcomes and mean differences for continuous outcomes. Subgroup analyses were planned by BMI category and by cancer histological type, stage, and grade. The authors contacted principal investigators of included trials to obtain unpublished data relevant to the review outcomes.
From 873 records screened, only three RCTs involving 161 overweight and obese women met the inclusion criteria. All three trials were conducted in US university hospitals and compared combined lifestyle and behavioural interventions (diet modification, increased physical activity, self-monitoring, and counselling) with usual care. No trials of pharmacological or surgical weight-loss interventions were identified.
The included trials were small, ranging from 37 to 75 participants, and all were of low or very low quality due to high risk of performance bias (impossible to blind participants to lifestyle interventions), unblinded outcome assessors, and significant loss to follow-up (attrition rates up to 29%). One trial had a three-arm design comparing two counselling formats with usual care. Intervention durations were approximately six months, with follow-up extending to 24 months in one study.
All participants had been previously treated for endometrial cancer with surgery as the primary treatment. Two RCTs included only stage I or II disease, while the third did not specify stage. The mean age of participants ranged from 54 to 62 years. All interventions combined dietary advice with physical activity recommendations and behavioural strategies to improve adherence.
Combined lifestyle and behavioural interventions showed no improvement in overall survival at 6, 12, or 24 months. At 24 months, the mortality risk ratio was 0.23 (95% CI 0.01 to 4.55, P = 0.34), based on a single RCT with 37 participants and very low-certainty evidence. However, this finding must be interpreted cautiously: so few deaths occurred that meaningful statistical comparison was impossible. No RCTs reported recurrence-free survival data.
There was no evidence that lifestyle interventions improved cancer-specific survival at any time point, as no cancer-related deaths were reported in either group across the included studies. Similarly, no cardiovascular or metabolic events (strokes, heart attacks, heart failure hospitalisations) were recorded at 6 or 12 months in any trial, making it impossible to assess the impact of weight-loss interventions on these important outcomes.
Regarding weight loss, the interventions were not associated with statistically significant weight change at 6 months (mean difference -1.88 kg, P = 0.37) or 12 months (mean difference -8.98 kg, P = 0.11). At 24 months in one RCT, super-obese participants (BMI over 40) did lose significantly more weight than controls, but this result was heavily influenced by two participants who underwent bariatric surgery during follow-up.
No life-threatening adverse events were reported in any of the included trials. However, lifestyle interventions were associated with a significantly higher risk of musculoskeletal symptoms including knee and leg pain and muscle weakness (RR 19.03, 95% CI 1.17 to 310.52, P = 0.04, two RCTs, 91 participants, low-certainty evidence). This is likely attributable to the increased physical activity component of the interventions.
Two participants reported episodes of diarrhoea that were felt to be possibly related to the dietary changes in the intervention, though overall the interventions were not associated with a statistically significant increase in diarrhoea risk. No serious hospitalisations or deaths were attributed to the weight-loss interventions in any of the trials.
Quality of life was measured using different instruments across the trials (SF-12 and FACT-G questionnaires), and no significant improvement was found at 6 or 12 months. The FACT-G scores showed a non-significant trend toward improvement at 6 months (MD 2.51, P = 0.54) and at 12 months (MD 2.77, P = 0.11). Baseline BMI did not affect the quality of life response in subgroup analyses.
The extremely limited evidence base reflects several structural challenges. Only three small trials met inclusion criteria, all focused exclusively on lifestyle and behavioural strategies. No pharmacological or surgical weight-loss interventions, which are generally more effective at achieving sustained weight loss, have been tested in this population through randomised trials. The short intervention duration (six months) and limited follow-up may have been insufficient to detect meaningful survival differences.
All included studies carried high risk of performance and detection bias because it is impossible to blind participants and providers to a lifestyle intervention. The use of unblinded outcome assessors in all trials may have affected subjective outcomes such as quality of life, though it is unlikely to have affected objective measures like weight and survival. Two of the three trials were from the same research group recruiting from the same hospital, limiting generalisability.
Using the GRADE framework, the certainty of evidence for all outcomes was rated as either low or very low, meaning the true effect is likely to be substantially different from the estimates in this review. Key reasons for downgrading included serious risk of bias, very small sample sizes leading to imprecise estimates with wide confidence intervals, and indirectness in one study where two participants underwent gastric bypass surgery during the intervention period.
The authors conclude that there is currently insufficient high-quality evidence to determine whether weight-loss interventions affect survival, quality of life, or meaningful weight change in endometrial cancer survivors. This is a striking gap given the established biological rationale linking obesity to worse outcomes and the rising incidence of obesity-related endometrial cancer.
Future research priorities include adequately powered RCTs with follow-up of 5 to 10 years examining pharmacological treatments (such as orlistat or appetite suppressants), bariatric surgery, and varying dietary modification regimens. Trials should include participants with both early and late stage disease, endometrioid and non-endometrioid subtypes, and should be designed with survival as a primary outcome rather than a secondary measure. Five ongoing trials were identified at the time of the review.
The increased musculoskeletal symptoms associated with exercise-based interventions highlight the need for carefully designed physical activity programs for this population. Despite the lack of demonstrated benefit in this review, weight-loss interventions remain biologically plausible as a strategy to reduce cardiovascular mortality and potentially improve cancer outcomes. The challenge is generating the rigorous evidence to confirm or refute this hypothesis.
This Cochrane review found that the true effect of weight-loss interventions in obese endometrial cancer survivors is currently unknown. The three included trials showed no benefit on survival, cancer-specific outcomes, weight loss, cardiovascular events, or quality of life, but the evidence was too limited and low-quality to draw firm conclusions in either direction.
The limited evidence does suggest that lifestyle interventions carry little risk of serious harm, though increased musculoskeletal complaints should be anticipated. The biological rationale for weight management in this population remains strong, with obesity driving cancer through oestrogen, insulin, and inflammatory pathways and simultaneously increasing cardiovascular mortality risk.
Until larger, methodologically rigorous trials with longer follow-up are completed, clinicians should continue to recommend weight management based on general health benefits while acknowledging that specific survival benefits in endometrial cancer remain unproven. The five ongoing trials identified in this review may begin to address this evidence gap in the coming years.