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SERMS act as antagonist for the activation function 2 (AF2) domain of the estrogen receptor. Another class classified as ICI 182,780 and ICI 164,384 are antagonists that can inhibit AF1 and activation function 2 (AF2) domains, therefore are known to be “pure” antiestrogens.

Estrogen receptors (ER) like ERα and ERβ include activation function 1 (AF1) domain and activation function 2 (AF2) domain in which SERMS act as antagonists for the AF2 domain while “pure” antiestrogens like ICI 182,780 and ICI 164,384 are antagonists for the AF1 and AF2 domains.

The first nonsteroidal antiestrogen was discovered by Lerner and coworkers in 1958.