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Original Investigation
April 2, 2020

Association Between Breastfeeding and Ovarian Cancer Risk

Author Affiliations
  • 1Obstetrics and Gynecology Epidemiology Center, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
  • 2Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts
  • 3Channing Division of Network Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
  • 4Department of Biostatistics, Harvard T. H. Chan School of Public Health, Boston, Massachusetts
  • 5Division of Population Sciences, Moffitt Cancer Center, Tampa, Florida
  • 6Population Health Department, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia
  • 7The University of Queensland School of Public Health, Brisbane, Queensland, Australia
  • 8Department of Chronic Disease Epidemiology, Yale School of Public Health, New Haven, Connecticut
  • 9Program in Epidemiology, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington
  • 10Department of Epidemiology, School of Public Health, University of Washington, Seattle
  • 11Department of Population Health Science, Huntsman Cancer Institute, University of Utah, Salt Lake City
  • 12Division of Cancer Epidemiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
  • 13Cancer Epidemiology Group, University Cancer Center Hamburg, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • 14Community and Population Health Research Institute, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, California
  • 15Cancer Prevention and Control, Samuel Oschin Comprehensive Cancer Institute, Cedars-Sinai Medical Center, Los Angeles, California
  • 16Department of Cancer Prevention and Control, Roswell Park Comprehensive Cancer Center, Buffalo, New York
  • 17School of Public Health, University of Texas Health Science Center at Houston, Houston
  • 18Department of Virus, Lifestyle and Genes, Danish Cancer Society Research Center, Copenhagen, Denmark
  • 19Rigshospitalet, Department of Gynaecology, University of Copenhagen, Copenhagen, Denmark
  • 20Department of Epidemiology, Rollins School of Public Health, Atlanta, Georgia
  • 21Department of Epidemiology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire
  • 22Cancer Prevention and Control Program, Rutgers Cancer Institute of New Jersey, New Brunswick
  • 23Department of Population Health Science and Policy, Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, New York
  • 24Department of Epidemiology & Population Health, Stanford University School of Medicine, Stanford, California
  • 25Epidemiology Center, College of Medicine, University of South Florida, Tampa
  • 26Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor
  • 27Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles
  • 28Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York, New York
  • 29Women’s Cancer Research Center, Magee-Womens Research Institute, Hillman Cancer Center, Department of Obstetrics, Gynecology and Reproductive Sciences, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
  • 30Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, Massachusetts
JAMA Oncol. 2020;6(6):e200421. doi:10.1001/jamaoncol.2020.0421
Key Points

Question  Is breastfeeding associated with risk of ovarian cancer overall and by histotype?

Findings  In this pooled analysis including 9973 women with ovarian cancer and 13 843 controls from 13 case-control studies, breastfeeding was associated with a 24% reduced risk of invasive epithelial ovarian cancer. Longer breastfeeding duration and shorter time since last breastfeeding episode were associated with a further decrease in risk.

Meaning  This large study with extensive information on breastfeeding provides epidemiological evidence that breastfeeding, a potentially modifiable factor, may confer significant reduction in ovarian cancer risk, including high-grade serous, the deadliest subtype.


Importance  Breastfeeding has been associated with a reduced risk of epithelial ovarian cancer in multiple studies, but others showed no association. Whether risk reduction extends beyond that provided by pregnancy alone or differs by histotype is unclear. Furthermore, the observed associations between duration and timing of breastfeeding with ovarian cancer risk have been inconsistent.

Objective  To determine the association between breastfeeding (ie, ever/never, duration, timing) and ovarian cancer risk overall and by histotype.

Design, Setting, and Participants  A pooled analysis of parous women with ovarian cancer and controls from 13 case-control studies participating in the Ovarian Cancer Association Consortium was performed. Odds ratios (ORs) and 95% CIs of the overall association were calculated using multivariable logistic regression and polytomous logistic regression for histotype-specific associations. All data were collected from individual sites from November 1989 to December 2009, and analysis took place from September 2017 to July 2019.

Exposures  Data on breastfeeding history, including duration per child breastfed, age at first and last breastfeeding, and years since last breastfeeding were collected by questionnaire or interview and was harmonized across studies.

Main Outcomes and Measures  Diagnosis of epithelial ovarian cancer.

Results  A total of 9973 women with ovarian cancer (mean [SD] age, 57.4 [11.1] years) and 13 843 controls (mean [SD] age, 56.4 [11.7] years) were included. Breastfeeding was associated with a 24% lower risk of invasive ovarian cancer (odds ratio [OR], 0.76; 95% CI, 0.71-0.80). Independent of parity, ever having breastfed was associated with reduction in risk of all invasive ovarian cancers, particularly high-grade serous and endometrioid cancers. For a single breastfeeding episode, mean breastfeeding duration of 1 to 3 months was associated with 18% lower risk (OR, 0.82; 95% CI, 0.76-0.88), and breastfeeding for 12 or more months was associated with a 34% lower risk (OR, 0.66; 95% CI, 0.58-0.75). More recent breastfeeding was associated with a reduction in risk (OR, 0.56; 95% CI, 0.47-0.66 for <10 years) that persisted for decades (OR, 0.83; 95% CI, 0.77-0.90 for ≥30 years; P for trend = .02).

Conclusions and Relevance  Breastfeeding is associated with a significant decrease in risk of ovarian cancer overall and for the high-grade serous subtype, the most lethal type of ovarian cancer. The findings suggest that breastfeeding is a potentially modifiable factor that may lower risk of ovarian cancer independent of pregnancy alone.

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    1 Comment for this article
    Backwards figures
    Jenny Allen |
    As usual the results are backwards, citing a reduced risk due to breastfeeding. However, breastfeeding is the biological norm, and should be used as the baseline, not breastfeeding is the deviation from the biological norm, so these results should be written as the increased risk of cancer from not breastfeeding.