1. Breastfeeding was found to be significantly associated with decrease risk of invasive ovarian cancer, including high-grade serous and endometroid cancer.
Evidence Rating: 2 (Good)
Ovarian cancer is a significant contributor to female mortality, with 5-year survival following diagnosis being less than 50%. Prevention is critical for reducing disease mortality, but currently, few modifiable risk factors beyond oral contraceptive use have been identified. Breast feeding has been reported as a potential modifiable risk factor, with some studies finding a negative association between breast feeding and epithelial ovarian cancer development. The relationship between the two is not well characterized however, as prior studies often had insufficient sample sizes. In this pooled analysis, data of 9973 women with ovarian cancer and 13 843 controls from the Ovarian Cancer Association Consortium was included to further investigate this association. Data was collected between 1989 and 2009, with exposures of interest including duration of breastfeeding, age at first and last breastfeeding, and years since last breastfeeding for example. A history of breastfeeding was associated with an overall 24% lower risk of invasive ovarian cancer (odds ratio [OR], 0.76; 95% CI, 0.71-0.80), and 28% reduction of borderline tumor risk, and was independent of parity. Among invasive diseases, researchers observed statistically significant associations 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 tumors (OR, 0.78; 95% CI, 0.64-0.96). The protective effect was more pronounced with greater duration of breastfeeding (18% risk reduction for 1 to 3 months, 34% reduction for 12 months or greater), and reduction of cancer risk persisted for decades, with significantly lower risk even 30 years later. This study represents the largest study investigating breastfeeding and ovarian cancer risk, providing strong evidence for breastfeeding as a potentially modifiable risk factor for cancer development. Future research to better characterize the biological mechanisms underlying risk reduction are encouraged to potentially reveal further therapeutic targets or screening measures related to ovarian cancer.