Role of Tamoxifen, Raloxifene, Anastrozole & Exemestane Tamoxifen, Raloxifene, Anastrozole and Exemestane efficiently prevent estrogen-receptor positive breast cancer. This type of breast cancer contributes two-thirds of all breast cancers. Tamoxifen & Raloxifene – belong to Selective Estrogen Receptor Modulators (SERMs). These drugs bind to estrogen receptors in breast tissue blocking the binding site for estrogen. Since estrogen is the key hormone in triggering the development of estrogen-receptor positive breast cancer therefore blocking binding of estrogen inhibits neoplastic onset. Anastrozole & Exemestane – belong to Aromatase Inhibitors (AIs). Aromatase is the key enzyme requires for the synthesis for estrogen. These drugs block aromatase enzyme inhibiting the synthesis of estrogen. As mentioned earlier, estrogen is the key hormone in triggering the development of estrogen-receptor positive breast cancer therefore blocking binding of estrogen inhibits neoplastic onset.