A chemical substance produced in the body that controls and regulates the activity of certain organs. With regard to breast cancer, the most important hormone is estrogen. Progesterone plays a lesser role. Breast cells, both normal and cancerous, can have “receptors” on their cells that can interact with estrogen in the blood stream. There are some breast cancer treatments that work by blocking this interaction on the surface of the cells.

A sudden wave of mild or intense body heat caused by rushes of hormonal changes resulting from decreased levels of estrogen. Hot flashes can occur at any time and may last from a few seconds to a half-hour. They are due to blood vessel opening and constricting and are often a symptom of menopause. Hot flashes sometimes are caused, or increased, by the use of tamoxifen, an estrogen blocking drug used in women with estrogen receptor (ER) positive cancer.

A condition in which there is an increase in the number of normal cells in a tissue or organ. This is often seen on breast biopsies, and does not have that much significance, unless the hyperplasia is considered “atypical”. In this case, although there is no cancer, the risk for developing cancer in the future is increased.