Androgens are thought to cause
prostate cancer, but there is little epidemiological support for this notion. Animal studies, however, demonstrate that
androgens are very strong
tumor promotors for prostate
carcinogenesis after
tumor-initiating events. Even treatment with low doses of
testosterone alone can induce
prostate cancer in rodents. Because
testosterone can be converted to
estradiol-17beta by the
enzyme aromatase, expressed in human and rodent prostate,
estrogen may be involved in
prostate cancer induction by
testosterone. When
estradiol is added to
testosterone treatment of rats,
prostate cancer incidence is markedly increased and even a short course of
estrogen treatment results in a high incidence of
prostate cancer. The active
testosterone metabolite 5alpha-dihydrotestosterone cannot be aromatized to
estrogen and hardly induces
prostate cancer, supporting a critical role of
estrogen in prostate
carcinogenesis.
Estrogen receptors are expressed in the prostate and may mediate some or all of the effects of
estrogen. However, there is also evidence that in the rodent and human prostate conversion occurs of
estrogens to
catecholestrogens. These can be converted to reactive intermediates that can adduct to
DNA and cause generation of
reactive oxygen species, and thus
estradiol can be a weak
DNA damaging (genotoxic)
carcinogen. In the rat prostate DNA damage can result from
estrogen treatment; this occurs prior to
cancer development and at exactly the same location.
Inflammation may be associated with
prostate cancer risk, but no environmental carcinogenic risk factors have been definitively identified. We postulate that endogenous factors present in every man, sex
steroids, are responsible for the high prevalence of
prostate cancer in aging men,
androgens acting as strong
tumor promoters in the presence of a weak, but continuously present genotoxic
carcinogen,
estradiol-17beta.