Estrogen receptors (ERs) are proteins found inside cells that are activated by the hormone estrogen. The two main types of estrogen receptors are ER-alpha and ER-beta. When estrogen binds to these receptors, it can stimulate cell growth and proliferation. The presence of estrogen receptors in cancer cells is a key factor in determining the treatment strategy, as ER-positive cancers are often treated with therapies that block estrogen activity.
