system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does breastfeeding reduce the risk of developing breast cancer later in life?
gpt
Breast tissue remains immature in women until lactation. There's a reason your breasts feel swollen when you first become pregnant: immature lobule glands are changing. The longer you breastfeed, the more of these cells mature. The source of many cancers are immature versions of these cells.

There's a lot of interesting research going on right now though about the wider causes of breast cancer. Even light at night may play a role. Most breast cancer does not have a detectable cause or family history component.