The donated milk was probably to blame: recent laboratory research on rats has shown that rats briefly exposed to the substances aflatoxin tend to develop liver cancer when fed casein, a milk protein.

All animal, bird, fish or egg derived protein plays a role in the formation and promotion of cancer, but the most potent so far is casein.

That's because casein is a difficult protein for human beings to digest, which is why it is present in smaller quantities in human breast milk.