Sara M. Tolaney, MD, MPH, states that all breast cancers should be tested for estrogen, progesterone, and HER2 receptors; HER2 testing involves an immunohistochemistry stain to quantify protein levels, with 3+ indicating HER2+ disease, 0 indicating HER2- disease, and 1-2+ levels needing additional FISH testing to clarify HER2 status.
