The T Colin Campbell Centre for Nutrition studies has deemed casein (cows’ milk protein) to be a carcinogen. Using standard FDA methodology for environmental toxins, different levels of casein were recorded along with levels of illness.
Quoting Campbell, “In our experiments over 25+ years, and published extensively, we showed that casein increased experimental cancer at levels within the range of human experience — with no need to estimate low level response in humans, from high level response in rats — and we know also know how it works! This suggested casein (and likely most other animal proteins) is a far more relevant carcinogen than any pesticide, herbicide, food additive or other noxious chemical ever tested.
Casein is found in a number of oncology drugs.
Ref: http://nutritionstudies.org/provocations-dairy-protein-causes-cancer/