AMERICAN CANCER SOCIETY ON rBGH. “The available evidence shows that the use of rBGH can cause adverse health effects in cows. The evidence for potential harm to humans is inconclusive. It is not clear that drinking milk produced using rBGH significantly increases IGF-1 levels in humans or adds to the risk of developing cancer.”
http://www.cancer.org/cancer/cancercauses/othercarcinogens/athome/recombinant-bovine-growth-hormone