Brian Leyland-jones, MD, PhD

Historically, breast tumor classification and therapeutic decisions have relied on immunohistochemical (IHC) techniques for characterizing biomarkers such as estrogen receptor (ER), progesterone receptor (PR), and the epidermal growth factor receptor 2 (HER2), as described in the review by Ma and colleagues. However, these markers have been found to be inadequate for fully predicting a patient’s response to a given breast cancer treatment such as endocrine therapy.