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Does Breastfeeding Affect Invasive Ovarian Cancer Risk?


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In a large pooled analysis reported in JAMA Oncology by Babic et al, breastfeeding was associated with a significant reduction in risk for invasive ovarian cancers, including high-grade serous disease.

“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.”
— Babic et al

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Study Details

The pooled analysis included data from 9,973 women with ovarian cancer and 13,843 controls from 13 Ovarian Cancer Association Consortium case-control studies, with initial data collection at consortium sites between November 1989 and December 2009. A single breastfeeding episode was defined as breastfeeding offspring from a given pregnancy. At time of analysis, mean ages were 57.4 years for women with ovarian cancer and 56.4 years for women in the control groups. Overall, 89% of participants identified as white. Among parous controls, prevalence of ever-breastfeeding ranged from 41% to 93% among studies.

Key Findings

On multivariate analysis, ever-breastfeeding vs no breastfeeding was associated with a significantly reduced risk of invasive ovarian cancer (odds ratio [OR] = 0.76, 95% confidence interval [CI] = 0.71–0.80), as well as decreased risk of borderline tumors (OR = 0.72. 95% CI = 0.64–0.81).

For invasive tumors, the association was significant for high-grade serous (OR = 0.75, 95% CI = 0.70–0.81), endometrioid (OR = 0.73, 95% CI = 0.64–0.84), and clear cell subtypes (OR = 0.78, 95% CI = 0.64–0.96).

For a single breastfeeding episode, significant reductions in risk were observed for mean breastfeeding durations of 1 to 3 months (OR = 0.82, 95% CI = 0.76–0.88) and for ≥ 12 months (OR = 0.66, 95% CI = 0.58–0.75; P for trend = .001).

Among primiparous women, ever-breastfeeding was associated with significantly reduced risk of all invasive disease (OR = 0.86, 95% CI = 0.75­–0.99) and high-grade serous disease (OR = 0.84, 95% CI = 0.71–0.99). Similar associations were observed for all invasive tumors and high-grade serous tumors among multiparous women.

More recent breastfeeding was associated with a significant reduction in risk for invasive disease (OR = 0.56, 95% CI = 0.47–0.66, for time since last breastfeeding of < 10 years) with reduction in risk still evident with time since last breastfeeding of ≤ 30 years (OR = 0.83, 95% CI = 0.77–0.90; P for trend = .02).

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.”

They also noted, “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.”

Naoko Sasamoto, MD, MPH, of the Obstetrics and Gynecology Epidemiology Center, Brigham and Women’s Hospital, is the corresponding author for the JAMA Oncology article.

Disclosure: The study was funded by the National Cancer Institute. For full disclosures of the study authors, visit jamanetwork.com.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
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