Researchers at Washington University in St. Louis, MO found some evidence suggesting that cancer patients can slow the growth of prostate cancer and breast cancer by up to 75% simply restricting intake of protein.   They also found that plant-derived protein is less capable of promoting cancer growth than animal-derived protein.

This study suggests that the very first thing cancer patients can do after diagnosis is using a low-protein vegetarian or vegan diet.  Some patients with prostate cancer or breast cancer who followed a raw vegetarian or vegan diet along with some supplemental intervention had their disease cured without resorting to conventional treatments such as chemotherapy and radiation. 

Dietary protein restriction inhibits tumor growth in human xenograft models of prostate and breast cancer

L Fontana, RM Adelaiye, AL Rastelli, KM Miles… - 2013 - digitalcommons.wustl.edu