Tamoxifen
Tamoxifen used to target estrogen-sensitive breast cancer cells is an important step on the path to curing this disease.
Credit: National Cancer Institute
October is National Breast Cancer Awareness month, an international project to bring attention to breast cancer, to raise funds for research and treatment, and to provide support for women who have been diagnosed with or have survived the disease. More than 1 in 8 women will be diagnosed with breast cancer at some point in their lives, and it is the second leading cause of cancer deaths in women behind lung cancer.
There are actually several different types of breast cancer, and determining the traits of the cancer in each individual patient is essential for planning the most effective treatment plan possible. Many cases of breast cancer are hormone sensitive; about 75 precent of breast cancers are estrogen receptor positive or ER+, which means that they grow in response to the presence of estrogen. Of those, 65 percent are also progesterone positive, or PR+. These types of cancers are very likely to respond well to hormone therapies, which are used following radiation and chemotherapy.
Tamoxifen has been used very effectively to treat ER+ breast cancers, although it is far less effective in cancers that are not sensitive to estrogen. An estrogen positive cancer cell is characterized by sites on the surface of the cell that are shaped like keyholes with all the right bumps and grooves to fit an estrogen molecule. When the estrogen arrives, it acts like a key in the keyhole of the receptor, which unlocks cell division. The active metabolite of Tamoxifen, 4-hydroxytamoxifen, fits into the lock of the estrogen receptor, but its different structure effectively ‘breaks the key off’ in the lock. The receptor is permanently blocked, cell division is not activated, and the cancer does not spread.
Since surgery to remove breast cancer tumors can never eliminate every cancer cell in the body, Tamoxifen can be used to find those remaining cells and prevent them from reestablishing or spreading the cancer. Tamoxifen is often administered after the rest of the treatment ends – even up to five years later – as an added insurance policy to complete a cure. It is not the 100 percent cure that is sought, but it is a step in the right direction.
Additional information about estrogen-sensitive cancers and Tamoxifen may be found at http://www.wcn.org/articles/treatment/hormone_therapy/estrogen_receptors/
This topic was adapted from the technology milestones project of 2001 ACS President Attila Pavlath.