Endoxifen E-isomer is primarily studied for its potential role in cancer treatment, particularly in breast cancer. It acts as a selective estrogen receptor modulator (SERM), which helps in blocking estrogen receptors in breast tissue, thereby inhibiting the growth of estrogen-sensitive tumors. This compound is considered a key metabolite of tamoxifen, a widely used drug in breast cancer therapy. Research is ongoing to explore its efficacy as a standalone treatment or in combination with other therapies to improve outcomes for patients with hormone receptor-positive breast cancer. Additionally, its application is being investigated in other estrogen-related conditions, such as endometriosis and certain types of infertility.