I'm just gunna copy and paste what I've come across trying to find something for my buddy who wants to increase his LBM, but infact has had prostate cancer and had prostate removed.
IGF-1 and cancer
BRISTOL, UNITED KINGDOM. Several studies have shown powerful associations between blood levels of insulin-like growth factor-I (IGF-1) and the risk of colon cancer, prostate cancer, and premenopausal breast cancer. As a matter of fact, recent evidence indicates that high IGF-1 levels may be more important than other previously reported risk factors for cancer. IGF-1 is released by human growth hormone and stimulates growth throughout fetal and child development. IGF-1 in the body is normally tightly bound to a large protein molecule (IGF binding protein-3) and there is evidence that high levels of IGF binding protein-3 protect against the development of certain cancers.
A distinguished group of medical researchers at the University of Bristol now voice concern about the increasing use of IGF-1 and growth hormone enhancers by body builders and elderly people trying to recapture their vanishing youth. They suggest that IGF-1 may increase both cell turnover and the susceptibility of cells to become cancerous. They also point to recent evidence that indicates that IGF-1 prevents the programmed death (apoptosis) of cancer cells. The researchers warn that people using growth hormone and IGF-1 enhancers are unlikely to be aware of their potentially harmful effects.
The pharmaceutical industry is well aware of the increasingly clear association between IGF-1 and cancer. Chemotherapeutic drugs are being developed to block the activity of IGF-1 or enhance the activity of IGF binding protein-3.
Smith, George Davey, et al. Cancer and insulin-like growth factor-I. British Medical Journal, Vol. 321, October 7, 2000, pp. 847-48 (editorial)