Estrogen plays a very distinct role in the breast changes throughout a lady's lifetime. For example, in the puberty age group where there's minimal to no estrogen being much produced at that point, the breast tissue's very dense. That's one main reason we don't do mammograms on ladies usually until they’re in their late 20’s-30’s, because it looks like a snow storm. It's so dense that you can't read it. However, as they then become actively menstruating and the estrogen levels are up and down, and they're maybe becoming pregnant, the breast tissue is very responsive to the estrogen molecule leading to increased breast duct development, increased lobules which are the parts in the end of the ductal system, and preparation for possible pregnancy. Of course, pregnancy itself leads to lots of changes, swelling of the breasts getting ready for that child, potentially breastfeeding.
Then the estrogen plays a role due to the lack of estrogen. As a lady goes through her menopausal phase of her life and the estrogen levels fall dramatically, then the breast tissue loses a lot of its integrity because it becomes fatty replaced. You can see that both on physical examination, you might see sagging of the breast because of that, and clearly on mammograms you'll see a difference as far as the density of the breast.
