In a pooled analysis reported in JAMA Oncology,1 Naoko Sasamoto, MD, MPH, of the Obstetrics and Gynecology Epidemiology Center, Brigham and Women’s Hospital, Boston, and colleagues found that breastfeeding, even for durations of 1 to 3 months per birth, was associated with a significant reduction in the risk for epithelial invasive ovarian cancers, including high-grade serous disease. As stated by the investigators, the study is, to their knowledge, the largest such analysis reported to date.
“Breastfeeding is a potentially modifiable factor that may lower risk of ovarian cancer independent of pregnancy alone….”— Naoko Sasamoto, MD, MPH, and colleagues
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The study was a pooled analysis of data from 9,973 parous women with ovarian cancer and 13,843 parous controls from 13 Ovarian Cancer Association Consortium case-control studies, with initial data collection at consortium sites occurring between November 1989 and December 2009. A single breastfeeding episode was defined as breastfeeding offspring from a given pregnancy. At the time of analysis, mean ages were 57.4 years for women with ovarian cancer and 56.4 years for controls. Overall, 89% of participants identified as white. Ever breastfeeding was reported by 5,981 cases (60%) and 9,417 controls (68%).
On multivariate analysis, ever breastfeeding vs no breastfeeding was associated with a significantly reduced risk of invasive ovarian cancer (odds ratio [OR] = 0.76), as well as a decreased risk of borderline tumors (OR = 0.72).
With regard to the potential mechanisms involved in the association between breastfeeding and reduced ovarian cancer risk, the investigators observed: “To date, the leading hypothesis has been that ovulation suppression during breastfeeding inhibits epithelial cell division and proliferation, thereby reducing the opportunity to initiate or promote carcinogenesis. This may especially be pertinent in the first few months postpartum, when immune function and tumor surveillance mechanisms remain suppressed…. However, we observed a stronger inverse association with longer breastfeeding duration. Several lines of evidence suggest that breastfeeding may also be associated with long-term modulation of inflammatory, immune, or metabolic pathways, which could influence ovarian cancer risk.”
The investigators concluded: “Breastfeeding is associated with a significant decrease in risk of ovarian cancer overall and for the high-grade serous subtype. The findings suggest that breastfeeding is a potentially modifiable factor that may lower risk of ovarian cancer independent of pregnancy alone…. The World Health Organization recommends exclusive breastfeeding for at least 6 months and continued breastfeeding with complementary foods for 2 or more years…. Our results support these recommendations, while noting that breastfeeding fewer than 3 months per child is still associated with significant ovarian cancer risk reduction.”
DISCLOSURE: The study was funded by the National Cancer Institute. For full disclosures of the study authors, visit jamanetwork.com.
1. Babic A, Sasamoto N, Rosner BA, et al: Association between breastfeeding and ovarian cancer risk. JAMA Oncol. April 2, 2020 (early release online).
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