A study headed by June Chan at Harvard University links the growth protein insulin-like growth factor type-1 (IGF-1) with prostate cancer, but many health professionals caution against drawing quick conclusions. Methods used by Chan to assess this risk, including adjustment for other prostate cancer risk factors like smoking and the cancer-protective protein IGFBP-3, lead to questions regarding the accuracy of the conclusions drawn from this study. According to growth hormone clinical researcher Dr. L.E. Dorman, "In my experience, PSA [a widely accepted marker for prostate cancer] levels consistently drop 50% over a period of a month or two of growth hormone secretagogue therapy." Growth hormone--popularized for its anti-aging effects--works by stimulating IGF-1 production.

Dorman, the co-author of Growth Hormone: Reversing Human Aging Naturally, also points out that IGF-1 is produced by cells of the immune system, which may be stimulated in the presence of cancer. "To conclude that IGF-1 stimulates the initiation of prostate cancer goes against everything that we know about its positive effects on the immune system, which protects against cancer. To make any substantial conclusions about the effects of these hormones on prostate cancer, a study should include the use of growth hormone therapy with prostate cancer patients."

Dr. L. Cass Terry, a long-time researcher of growth hormone notes the complete lack of cancer incidence in any of his growth hormone treated patients, "With 800 people over the age of about 40, you would think that given the 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". Terry and his associate Dr. Edmund Chein report the results of growth hormone treatment on a man who came to them with prostate cancer, indicating that without any usual forms of treatment like surgery, the patients' levels dropped from the 50 to 60 range down to 5 to 7 (men with prostate cancer usually show levels of PSA in the 10 to 20 range). It has been hypothesized that these effects come from stimulatory effects on the immune system that result from growth hormone therapy.

Pharmacologist James Jamieson, who headed the development of a growth hormone secretagogue, notes the importance of using growth hormone therapy in a way that keeps IGF-1 within a healthy range. "When stimulated to release growth hormone, the body has mechanisms that typically keep IGF-1 within a normal range."