A selective androgen receptor modulator, or SARM, is a class of compound that can bind to the androgen receptor, but is not actually a steroid hormone.
Our SARMs are non-steroidal molecules that target and modulate the activity of androgen receptors within the cell on the nuclear membrane. The SARM binds to the androgen receptor, and then can interact with a receptor-specific segment of DNA that controls gene expression. The binding of a SARM with its nuclear hormone receptor can either activate or inhibit the nuclear activity because it can either block or stimulate the same nuclear hormone receptor under different conditions.
In the case of ER+AR+ breast cancer for example, it is believed that the SARM-AR complex can compete with the binding of estrogen receptor to hormonally responsive DNA sites, and inhibit the transcription of ER-responsive genes.