[kmm]

Protein shakes and workouts wouldn't lead to a higher rate of cell division in the breast, would it? Those cells just go through their natural turnover, influenced mostly by estrogen (which actually has been suspected to play a role in causing breast cancer: https://pubmed.ncbi.nlm.nih.gov/17113977/ )

If anything, you'd expect cancer of the muscle, myosarcoma, to be involved with muscle growth, which thankfully is really rare. Possibly because muscle growth is mostly a matter of hypertrophy of the muscle fibers, not the growth of more muscle cells.

I'd be surprised if the very real health benefits of staying active didn't way outweigh the possibly increased risk of cancer due to increased cell activity.

[voisin]

Isn’t whey, as a milk base, full of growth hormones meant for baby cows?