A study published in the British Journal of Cancer in 2000 found that "intake of protein rich in essential amino acids was positively associated with serum IGF-I." IGF-1 has been shown in many studies to increase hormonal (like prostate and breast) cancer rates. I wonder if protein loading is a good idea at all, especially since its never been shown to increase muscle mass, which would be an easy thing to show in a trial if it worked.
Allen NE, Appleby PN, Davey GK, Key TJ. Hormones and diet: low insulin-like growth factor-I but normal bioavailable androgens in vegan men. Br J Cancer. 2000 Jul;83(1):95-7.
IGF-1 is definitely something to be concerned with, it is a cancer causing just as you state. But it is my understanding that protein from plant sources does not raise IGF-1, that is animal protein that does the raising. But i may be wrong on this, are there studies that show otherwise that you know of?