Summary of resistance mechanisms and therapeutic approaches in metastatic ER+ breast cancer

Breast cancer is a prevalent malignant tumor in worldwide and it has been a prime challenge for public health. The development of this cancer is close related to drug use, breast cancer susceptibility genes, and diet. It can be categorized into four groups, which are 1. estrogen-containing receptor (ER+); 2. progesterone receptor (PR+); 3. with one or both receptors (HR+) and 4. HR- without these receptors. Estrogen receptor-positive breast cancers, ER+, are commonly produced when the level of estrogen in the breast cancer is higher than that which helps the cancer to grow and spread.[1] ER+ breast cancers have receptors and can use estrogen to grow, so common treatments are usually surgery and hormone therapy. This study will describe the mechanisms of endocrine therapy, the reasons why tumors become resistant to endocrine therapy, the progress made in recent years in overcoming resistance to endocrine therapy as well as suggesting undiscovered tactic to overcome this resistance in the future.