Breastfeeding Lowers the Risk of Ovarian Cancer

Women who breastfeed are at a significantly lower risk of ovarian cancer, including high-grade tumors, according to study findings published in JAMA Oncology, regardless of how long they did so.

“Numerous studies have investigated the association between breastfeeding and ovarian cancer risk, with some showing a significant decrease in risk and others showing no association,” the researchers wrote.

Therefore, they decided to examine any associations between breastfeeding and epithelial ovarian cancer risk overall using data from 13 Ovarian Cancer Association Consortium studies with information on breastfeeding history.

The entire analysis included nearly 24,000 women — 9,973 with ovarian cancer who were a median age of 57.4 years and 13,843 women who were a median age of 56.4 years and served as a control group. Most (89%) of the participants were white. Breastfeeding prevalence ranged from 41% to 93% among the control group and the mean duration for breastfeeding ranged from 3.4 to 8.7 months.

Compared with controls, women with ovarian cancer were older, more likely to be postmenopausal, had given birth to only one child, had never used oral contraceptives, had a history of endometriosis and had a family history of ovarian cancer.

Researchers learned that breastfeeding was associated with a 24% lower risk of invasive ovarian cancer and 28% decrease in borderline tumor risk. In those women who had ever breastfed, there was a reduction in risk of all invasive ovarian cancers, particularly high-grade serous and endometrioid cancers. For participants who breastfed from one to three months, there was an 18% lower risk and a 34% lower risk in those who breastfed for a year or more.

“Statistically significant risk reduction associated with a mean breastfeeding duration of fewer than three months per episode suggests even a short duration of breastfeeding is beneficial,” the researchers wrote. “The World Health Organization recommends exclusive breastfeeding for at least six months and continued breastfeeding with complementary foods for two or more years. Our results support these recommendations.”

The researchers also explained some biological mechanisms that could play a role in why breastfeeding reduces ovarian cancer risk. For example, experts have looked at ovulation suppression during breastfeeding which inhibits epithelial cell division that may reduce the risk of cancer forming, which may be especially true in the first few months after giving birth when immune function and tumor surveillance mechanisms remain suppressed, the researchers explained.

“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 researchers wrote.

Although the researchers touted the large sample size to enable them to evaluate breastfeeding patterns, they noted a few limitations to the study, such as the participants being predominantly white. Because of this, the details of breastfeeding patterns in black and Asian women, as well as other racial and ethnic groups could not be observed.