Breastfeeding Tied to Lower Breast Cancer Odds in Ethiopian Meta-Analysis

A pooled analysis of eight case-control studies involving 2,314 Ethiopian women has found that women with breastfeeding experience had 26 percent lower odds of breast cancer, while a history of abortion and oral contraceptive use were each associated with increased odds of the disease. The work, published as a systematic review and meta-analysis in Discover Medicine, is the first comprehensive synthesis of reproductive risk factors for breast cancer conducted specifically for Ethiopia, where breast cancer is the most commonly diagnosed cancer among women and the leading cause of cancer-related death in that group.

The research team searched PubMed/Medline, Scopus, Web of Science, ScienceDirect and the Google Scholar search engine up to April 10, 2026, following PRISMA 2020 guidelines. From 201 initially retrieved records, the screening process removed 115 duplicates, 59 inconsistent with the review, three of poor quality, two with inaccessible full texts, and 14 that did not report the outcome of interest. Eight full articles—six published and two unpublished—survived critical appraisal with the Joanna Briggs Institute checklist for case-control studies, scoring between 6 and 8 out of 10, and entered the final meta-analysis. Data were extracted independently by two reviewers using a standardized form, and pooled estimates were computed in Stata version 17 with a random-effects model.

The included studies were all case-control designs. Five originated in Addis Ababa, the country’s largest center for cancer diagnosis and treatment, two from the Sidama region and one from the Amhara region. All eight studies assessed breastfeeding; five examined oral contraceptive use and five examined abortion history. The exposures were defined as ever versus never breastfeeding, ever versus never use of oral contraceptives, and a history of at least one terminated pregnancy, whether induced or spontaneous.

The headline result concerned breastfeeding. Across eight studies, the pooled odds ratio was 0.74 (95 percent confidence interval 0.59 to 0.92), which the authors interpret as a 26 percent reduction in breast cancer odds among women who had breastfed. Heterogeneity for this outcome was reported as essentially absent, with an I-squared value of 0.00. The authors suggest the protective association may reflect hormonal and physiological effects of lactation, including reduced circulating estrogen and progesterone, enhanced estrogen excretion, and terminal differentiation of breast epithelial cells, though they note that one study among women in Iran reported a contradictory finding, possibly due to differences in sample size, design or population characteristics.

Abortion history showed the strongest positive association. Five studies yielded a pooled odds ratio of 2.22 (95 percent confidence interval 1.17 to 4.22), meaning women with a history of abortion had 122 percent higher odds of breast cancer in these data. However, this estimate came with substantial statistical heterogeneity—an I-squared of 84.23 percent—indicating wide variability among the underlying studies. Meta-regression using sample size and study year as covariates found no statistically significant explanation for that variability. The authors propose a biological rationale drawn from prior literature: a completed pregnancy drives breast cell proliferation followed by differentiation, which is thought to reduce susceptibility to carcinogenesis, whereas early pregnancy termination may leave proliferated epithelial cells undifferentiated and more vulnerable to carcinogenic stimuli. They also caution that their analysis did not distinguish induced from spontaneous abortion, or the number of episodes.

Oral contraceptive use was associated with a more modest elevation. Five studies produced a pooled odds ratio of 1.40 (95 percent confidence interval 1.02 to 1.98), with moderate heterogeneity (I-squared 43.84 percent). Because the lower confidence bound sits just above the null value of 1, the authors describe the estimate as borderline and imprecise. They frame this result within the broader observational literature, in which oral contraceptive use has been linked to increased risks of breast and cervical cancer alongside reduced risks of endometrial and ovarian cancer, and they explicitly state that observational data cannot establish whether an exposure such as oral contraceptive use causes or prevents cancer.

The certainty of the evidence, graded with the GRADE framework, is a crucial caveat. Certainty for the breastfeeding finding was rated low despite consistent and reasonably precise results. For abortion history, certainty was very low owing to the substantial heterogeneity and imprecision, and for oral contraceptive use it was very low because of the borderline confidence interval. Egger’s regression tests found no statistically significant publication bias for any of the three outcomes, with p-values of 0.461 for breastfeeding, 0.425 for oral contraceptive use and 0.34 for abortion history.

The authors list several limitations that temper interpretation. All primary studies relied on retrospective self-reports of reproductive history, which are vulnerable to recall bias and may distort reported abortion histories in particular. Every included study was case-control, a design less robust than prospective cohort work, and control recruitment was hospital-based, raising the possibility of selection bias if cases and controls differed in healthcare-seeking behavior. The pooling of induced and spontaneous abortions, the high heterogeneity for the abortion outcome, residual between-study differences despite the random-effects model, the small number of studies for some outcomes, and the restriction to English-language publications all add uncertainty. The authors state that the findings should be interpreted with caution.

Context matters for why these results drew attention. Globally, breast cancer accounted for 12.5 percent of cancer cases in the general population and 25.8 percent of cancer cases among women in 2022, and the International Agency for Research on Cancer estimated more than 2.26 million new cases and 685,000 deaths worldwide in 2020. In Ethiopia, breast cancer accounts for an estimated 15,244 cases—22.6 percent of all cancer diagnoses—and 8,159 cancer-related deaths among women annually, with an age-standardized incidence rate of 40.6 per 100,000 females. Studies cited by the authors report a steady rise in incidence and hospital admissions across Ethiopian regions, and more than half of global breast cancer incidence and deaths occur in low- and middle-income countries, where limited access to care, diagnostic errors and treatment costs compound the burden.

The authors conclude that the findings support strengthening public health interventions that promote breastfeeding and expanding awareness and counseling around reproductive health, while calling for large-scale, high-quality prospective studies to confirm the associations. Because all pooled estimates derive from observational case-control data, they represent associations rather than demonstrated causal effects, and the low to very low certainty ratings mean the numerical estimates—particularly for abortion and oral contraceptive use—may change as better evidence accumulates. For now, the synthesis offers Ethiopian policymakers the first locally grounded quantitative picture of how reproductive factors correlate with breast cancer risk in the country’s population, alongside a clear map of where the evidence base remains thin.

Subject of Research: Reproductive health factors associated with breast cancer risk among women in Ethiopia

Article Title: Systematic review and meta analysis of reproductive health factors associated with breast cancer among women in Ethiopia

Article References: Mekonen, H., Malkamu, B., Alemayehu, M. A., Teym, A., Temesgen, A., Bayeh, G. M., Yeshiwas, A. G., Anteneh, R. M., Yemata, G. A., Shimels, T., Yenew, C., Ayele, W. M., Ahmed, A. F., Kassa, A. A., Tsega, T. D., Ayalew, C. A., Tsega, S. S., Yigzaw, Z. A., Ejigu, A. G., … Mekonnen, B. A. (2026). Systematic review and meta analysis of reproductive health factors associated with breast cancer among women in Ethiopia. Discover Medicine, 3(1), Article 151. https://doi.org/10.1007/s44337-026-00722-5

Image Credits: AI Generated

DOI: 10.1007/s44337-026-00722-5

Keywords: breast cancer, Ethiopia, meta-analysis, breastfeeding, oral contraceptives, abortion, reproductive health, case-control studies, public health, epidemiology, heterogeneity, GRADE certainty