The growth and spread of breast cancer can be difficult to grasp because cancer cell growth is often fueled by normally healthy chemicals of the body, like estrogen, progesterone, and the HER2/neu gene (a growth hormone). Although each of these three bodily chemicals can serve an important healthy function, when a cell becomes cancerous these chemicals can accelerate the growth of breast cancer tumors.
Healthy HER2 receptors are the proteins that help manage how a breast cell grows, divides, and repairs itself. However, in about a quarter of all breast cancer patients, the HER2 gene isn’t functioning properly. It makes an excess number of copies of itself in a process known as “HER2 gene amplification.” Then these extra genes instruct the cells to make too many HER2 receptors, which is called “HER2 protein overexpression.” The ultimate result is that breast cells grow and divide in an uncontrolled fashion.