The ELAINE-3 study is seeking patients with ER-positive/HER2-negative metastatic breast cancer. Metastatic means the cancer has spread from the breast to other parts of the body. Metastatic breast cancer is also called “stage IV” cancer.
Estrogen receptors are proteins in or on the cells that can attach to estrogen in the blood when it gets close enough. When estrogen binds to the estrogen receptor, the receptor activates (turns on). When two activated estrogen receptors join together, they turn on genes that signal for cells to grow and divide. Estrogen receptors are found in healthy breast cells and breast cancer cells. Too many estrogen receptors can cause uncontrolled growth of breast cancer cells. Treatment with anti-estrogen hormone (endocrine) therapy can block the growth of the cancer cells.
Breast cancers that have estrogen receptors are called ER-positive (ER+) cancers. These cells may need estrogen to grow. These cells may stop growing or die when treated with substances that block the binding and actions of estrogen.
HER2-negative means the cancer cells do not create a protein called HER2, which makes cancer cells grow more quickly.
Hormone therapies (also called endocrine therapies) either stop the body from making estrogen or stop estrogen receptors from working, so the cancer cells cannot grow and divide.1 Because ER-positive cancer cells need the hormone estrogen to grow and divide, blocking estrogen is one way to treat them.
Over time, though, the genes inside cancer cells mutate (change), and a hormone therapy that used to work does not work anymore. This is called treatment resistance. ESR1 mutations may cause treatment resistance to certain types of hormone therapy.2
Estrogen receptor 1 (ESR1) gene mutations (changes) can evolve during hormone therapy. These mutations cause estrogen receptors to stay activated (leading to signals for the cell to grow and divide), even when there are no estrogens around. This means hormone therapy that blocks estrogen may not affect these cells.3,4
References: 1. Reinert T, Saad ED, Barrios CH, Bines J. Front Oncol. 2017;7:26. 2. Jesselsohn R, Buchwalter G, De Angelis C, Brown M, Schiff R. Nat Rev Clin Oncol. 2015;12(10):573-583. 3. Brett et al. Breast Cancer Res. 2021;23:85. 4. Herzog SK, et al. Br J Cancer. 2022;126:174-186.
