The attached & links below describes how oxidative stress plays a key role in Cancer.
One of glutathione's crucial roles is to mediate free radical damage.

 The Use of a Whey Protein Concentrate in the Treatment of Patients with Metastatic Carcinoma: A Phase I-II Clinical Study

 Whey proteins in cancer prevention

 Dietary milk proteins inhibit the development of Dimethylhydrazine-induced malignancy

 Dietary whey protein inhibits the development of dimethylhydrazine induced malignancy

 Whey protein concentrate (WPC) and glutathione modulation in cancer treatment

 Enhancing effect of patented whey protein isolate (Immunocal) on cytotoxicity of an anticancer drug

 Nutriceutical modulation of Glutathione with a humanized native milk serum protein isolate, Immunocal: application in AIDS and cancer

 The antioxidant system

 Glutathione System in Defense of Prostate Problems

 Molecular pathogenesis and prevention of prostate cancer.

 Effect of supplementation with a cysteine donor on muscular performance

 Antioxidants and Cancer Prevention Fact Sheet - National Cancer Institute

 Low colonic glutathione detoxification capacity in patients at risk for colon cancer

 The glutathione biotransformation system and colorectal cancer risk in humans

 Whey Protein Published Medical Articles Abstract Summary