Oncology

Breast cancer develops when breast tissue cells grow abnormally and multiply. In essence, the hormones-- estrogen and progesterone-- and excess levels of human epidermal growth factor receptor 2 (HER2) protein are the known drivers of breast cancer. By testing samples of breast cancer tissue for hormone receptors and HER2 levels, doctors can recommend therapies that work by reducing the strength of these drivers. Normally, around two-thirds of breast cancers will test positive for either estrogen or progesterone receptors, or both. About 20 percent will test positive for excess HER2. However, in 12–17 percent of people who receive a breast cancer diagnosis, the test w...