Breastfeeding and Endometrial Cancer Risk: An Analysis From the Epidemiology of Endometrial Cancer Consortium

Abstract

Objective: To investigate the association between breastfeeding and endometrial cancer risk using pooled data from 17 studies participating in the Epidemiology of Endometrial Cancer Consortium.

Methods: We conducted a meta-analysis with individual-level data from three cohort and 14 case-control studies. Study-specific odds ratios (ORs) and 95% confidence intervals (CIs) were estimated for the association between breastfeeding and risk of endometrial cancer using multivariable logistic regression and pooled using random-effects meta-analysis. We investigated between-study heterogeneity with I and Q statistics and metaregression.

Results: After excluding nulliparous women, the analyses included 8,981 women with endometrial cancer and 17,241 women in a control group. Ever breastfeeding was associated with an 11% reduction in risk of endometrial cancer (pooled OR 0.89, 95% CI 0.81-0.98). Longer average duration of breastfeeding per child was associated with lower risk of endometrial cancer, although there appeared to be some leveling of this effect beyond 6-9 months. The association with ever breastfeeding was not explained by greater parity and did not vary notably by body mass index or histologic subtype (grouped as endometrioid and mucinous compared with serous and clear cell).

Conclusion: Our findings suggest that reducing endometrial cancer risk can be added to the list of maternal benefits associated with breastfeeding. Ongoing promotion, support, and facilitation of this safe and beneficial behavior might therefore contribute to the prevention of this increasingly common cancer.

Figure 1

Forest plot showing study-specific estimates and 95% confidence intervals (CI) for the association between ever-breastfeeding and endometrial cancer risk amongst parous women. Estimates are stratified by study design (case-control/cohort) and ordered smallest to largest. The box size indicates the study weight, the line represents the 95% confidence interval, and the diamonds represent the pooled estimates. Higher I² values and P values <.05 suggest statistically significant between-study heterogeneity. Study acronyms are defined in Table 1.

Figure 2

Pooled odds ratios (OR) and 95% confidence intervals (CI) for the association between ever-breastfeeding and endometrial cancer risk stratified by participant characteristics. The number of studies included in each stratum varies because some studies did not have information on the variable of interest or because there were too few women in specific strata to calculate study-specific estimates. ^aOnly case group was stratified. ^bIncludes five studies in which all women were white. ^cIncludes one study in which all women were black. ^dIncludes one study in which all women were Asian. ^eThe estimate for ever breastfed in women born before 1950, including only the 11 studies that also included women who were born after 1950 is 0.93 (95%CI 0.84–1.03).