Probable: The factor is likely to be associated with increased or decreased risk of endometrial cancer, but the evidence is not as strong as for convincing. Decreases risk

Breastfeeding is probably associated with a decreased risk of endometrial cancer.

The longer a woman breastfeeds, the lower her risk of endometrial cancer. The risk of endometrial cancer decreases by about 3% for every 3 months a woman breastfeeds.

The protective effect of breastfeeding is likely to be due to hormonal changes. When a woman is producing milk and breastfeeding, the level of the female hormone oestrogen in her body is lower. This slows the growth of endometrial cells and can reduce the risk of endometrial cancer.