Hello there.  I can understand your concern.  Many people are taking collagen supplements. It supposedly gives you a better and firmer skin, increases bone strength and better hair and nails. The most common side effects are 1. Some people have a bad taste in their mouth for about an hour or so. 2. Decreased appetite in some. 3. Allergies if someone is sensitive. I havent come across cancer as a side effect. If you are scared then better not take. Best regards.  Dr. Anil kumar jain. Bangalore.