Subtypes of Breast Cancer

Breast cancer is a genetically and clinically heterogeneous disease with multiple subtypes. The classification of these subtypes has evolved over the years. The most common and widely accepted classification of breast cancer is from an immunohistochemical perspective, based on the expression of the following hormone receptors: estrogen (ER), progesterone (PR) and human epidermal growth factor (HER2). Accordingly, the following four subtypes of breast cancer are widely recognized: luminal A, luminal B, HER2-positive, and triple negative. With the recent advances in cancer research, and an increased molecular understanding of breast cancer, the current clinical model for classification of breast cancer may be benefit from the addition of several molecular markers such as miRNAs (let-7, miR-155, miR-150, miR-153) and mutations (p53, BRCA 1 and 2 genes).  This chapter provides an overview of the characteristics of these four subtypes of breast cancer.