Based on existing research, growth hormone does not cause cancer. Proof of this is the work by doctors Chen and Terry. They manage the clinic that conducted the HGH therapy. From 1994 to 1996, they treated more than 800 patients and received growth hormone injections, but none of the patients reported cancer. Here is a quote from Dr. Terry from the book Grow Young with HGH: "With 800 people over the age of about 40, you would think that given normal incidence rate of cancer, some of these people would get cancer. It could be that there is some sort of protective effect from growth hormone replacement ". However, if you already have a cancerous tumor, then you should never use growth hormone - it will cause its faster growth, therefore it is important to undergo medical examinations before starting HGH treatment.