Several studies have been conducted to investigate the association between breastfeeding and ovarian cancer; some show a positive association, and some show no association at all. This study aims to determine the exact association between breastfeeding and the risk of ovarian cancer. 

This is a pooled analysis that included a total of 9,973 parous women with ovarian cancer (mean age 57.4) and 13,843 control women (mean age 56.4) from 12 case-controlled studies. The risk of ovarian cancer was calculated using odds ratios, multivariable logistic regression, polytomous logistic regression. The data on breastfeeding history, including duration per breastfed child, age, and years since the last breastfeeding was taken into consideration. The primary outcome of the study was the diagnosis of epithelial ovarian cancer.

Breastfeeding was associated with a 24% lower risk of invasive ovarian cancer. A single breastfeeding episode with the mean breastfeeding duration of 1-3 months was associated with an 18% lower risk of ovarian cancer. Breastfeeding for 12 months or more was linked with a 34% lower risk of cancer, and recent breastfeeding had risk reduction effects that persisted for decades.

The research concluded that breastfeeding was associated with a substantial decrease in the risk of ovarian cancer of all types.