The male hormones are androgens, of which, like oestrogens, there are three: testosterone (the most potent), dehydroepiandrosterone (DHEA) and androstenedione (both weaker forms). The cortex of the adrenal gland is the site for the production of these hormones in small quantities in both sexes, but the main source in males is the testes. Androgens have masculinisation effects on a number of tissues. For example, they build muscle and bone by inducing cell and tissue growth, and so are sometimes abused by athletes and body builders (they are sometimes known as anabolic steroids) (Marieb 2001). These effects are seen during male puberty, when testosterone levels rise and growth accelerates. It is this cellular growth effect that is a problem in a number of male tumours that respond to androgens. Testosterone and the other hormones bind to androgen receptors (AR) in cells that are androgen receptor positive (AR, similar to ER in women, see p. 174). Any male tumour that is AR will grow faster with androgen stimulation, and treatment with an oestrogen causes the tumour to regress.