Although extremely rare, male breast cancer has been associated with the administration of testosterone. It is unknown, however, if the hormone therapy was related to the onset of this disease, or if it was just incidental to its progression and discovery. Androgens generally exhibit inhibitory effects on hormone-responsive breast cancers, and have actually been used in their treatment. Estrogens, on the other hand, can support the growth of many breast tumors. It is not uncommon for elevated estrogen levels to result from testosterone therapy, and at least a supportive role is plausible. The exact relationship between isolated cases of breast carcinoma and testosterone administration in men remains unclear. Testosterone is presently contraindicated in patients with breast cancer.
The data concerning the effects of anabolic/androgenic steroids on insulin sensitivity is difficult to interpret. It does appear that when these drugs are used initially, reductions in body fat are common, particularly visceral adipose tissue. This may actually improve insulin sensitivity and the overall metabolic state, and reduce certain specific risk factors for diabetes and cardiovascular disease. Beyond this, the effects of AAS on glucose metabolism are not fully understood, and difficult to predict. Studies using supratherapeutic doses of testosterone and nandrolone have failed to produce any negative changes, suggesting that moderate AAS abuse is probably not associated with impairments in insulin sensitivity. At the same time, studies do suggest that there could be concerns with heavy steroid abuse. Further research is needed is assess the impact of steroid abuse on metabolic health.
Wlliam Llewellyn (2011) - Anabolics