This claim is based of a study conducted in India by Madhavan and Gopalan called “The effect of dietary protein on carcinogenesis of aflatoxin”. Aflatoxin is a carcinogen that the lab rats were exposed to in the study. The rats were then divided into two groups; one group was fed five percent casein while the other group was fed twenty percent casein. According to the film, the study found that the rats that were fed twenty percent casein had many cancerous growths and tumors. However, the rats fed only five percent casein either did not have any cancerous growths or they had very limited amount of cancerous growths.
Original Youtube video here: Looking For Information On Casein And Cancer