HER2 Reader is a simple clinical decision support app developed primarily for pathologists and oncologists who perform predictive marker testing for breast cancer. In October 2013, the American Society of Clinical Oncology (ASCO) and College of American Pathologists (CAP) published updated recommendations for HER2/neu testing by immunohistochemistry (IHC) and in situ hybridization (ISH), significantly modifying the interpretation criteria outlined in 2007. HER2 Reader will assist providers in adopting these new recommendations, as well as the 2010 ASCO/CAP recommendations for estrogen receptor (ER) and progesterone receptor (PgR) testing.