breastfeeding and breast cancer

I've always known that breastfeeding can greatly decrease your risk of breast cancer but I never really knew why. I was reading the Motherwear Catalog Blog today and found this information very interesting:

There are several hypotheses about why breastfeeding provides protection against breast cancer but at this time we do not know which is/are correct. The simplest explanation is that for many women the longer they breastfeed the fewer menstrual cycles they experience. Since with every menstrual cycle cells in the breast grow and divide and could by chance accumulate mutations which might lead to cancer, reducing the total number of cycles a woman experiences in her lifetime should lead to a decreased risk of breast cancer. This is supported by data showing that younger age at time of first menstruation and older age at menopause (greater total number of years menstruating) is associated with an increased risk of breast cancer. Another hypothesis is that breastfeeding results in a permanent change in either breast morphology or the expression of genes in the breast, and that this change provides protection against breast cancer. Finally it has been suggested that breastfeeding reduces the level of pollutants in the breast that may be associated

I also read that not only does it decrease your chances by 28%, but to have a baby and not breastfeed increases your rates by 39%!

Just some food for thought.