Breastfeeding Tied to Lower Risk of Ovarian Cancer, Including Lethal Subtype

By Marilynn Larkin

April 13, 2020

NEW YORK (Reuters Health) - Breastfeeding was associated with a significant decrease in ovarian cancer risk overall, as well as for high-grade serous tumors, the most lethal subtype, in a pooled analysis of case studies.

"Importantly, this (breastfeeding) benefit extends beyond any benefit of pregnancy alone," Dr. Naoko Sasamoto of Brigham and Women's Hospital in Boston told Reuters Health in an email on behalf of the authors. "Interestingly, an average duration of breastfeeding of less than three months was associated with significant reduction in risk, suggesting that even a short duration of breastfeeding may be beneficial."

The team analyzed parous women with ovarian cancer and controls from 13 case-controlled studies from the Ovarian Cancer Association Consortium. The women's mean age was about 57 and most (89%) were white.

As reported in JAMA Oncology, compared with controls, women with ovarian cancer were older, more likely to be postmenopausal and primiparous, to have never used oral contraceptives, and to have a history of endometriosis and a family history of ovarian cancer.

After adjustment and independent of parity, ever having breastfed was inversely associated with risks of both invasive (odds ratio, 0.76) and borderline (OR, 0.72) tumors compared with never having breastfed.

Specifically, among invasive tumors, the association was statistically significant for high-grade serous (OR, 0.75), endometrioid (OR, 0.73), and clear cell tumors (OR, 0.78).

Similar but nonsignificant associations were seen for low-grade serous tumors; however, no significant inverse association was observed for formucinous tumors.

For borderline tumors, a statistically significant inverse association was seen for both mucinous (OR, 0.68) and serous (OR, 0.77) tumors.

For a single breastfeeding episode, a mean duration of one to three months was associated with an 18% lower risk (OR, 0.82), whereas breastfeeding for 12 or more months was associated with a 34% lower risk (OR, 0.66).

Compared with women who never breastfed, less than 10 years from the last breastfeeding episode was associated with a 44% lower risk (OR, 0.56), while 30 years or less was associated with a 17% lower risk (OR, 0.83).

Dr. Sasamoto said, "While replication of our findings in prospective cohort studies is warranted, (they) add to the list of health benefits of breastfeeding. We hope these findings would support mothers who choose to breastfeed and clinicians who care for pregnant and nursing women. In addition, we hope (they) will support policies to build supportive environments for mothers who choose to breastfeed."

Dr. Kecia Gaither, Director of Perinatal Services at NYC Health and Hospitals/Lincoln, called the study "novel," but noted in an email to Reuters Health that it was limited by a lack of diversity in the study population. "It certainly serves as a great starting point for further research, hopefully stratifying not only population diversity, but including women with a strong family history of ovarian cancer, obese women, use of oral contraceptive pills and women with diabetes."

SOURCE: JAMA Oncology, online April 2, 2020.