Biomarkers in Breast Carcinomas

Invasive breast cancer is the most common malignancy in women and is an extremely heterogeneous disease. In addition to the morphologically defined subtypes, recently, gene expression profiling studies have provided molecular classification of breast cancer. Thus, luminal A and B, human epidermal growth factor receptor 2 (HER2)-enriched, and basal-like breast cancers constitute the majority of tumors. Biomarkers provide valuable diagnostic and prognostic/predictive information in these tumors. Estrogen receptor (ER), progesterone receptor (PR), and HER2 are the most widely used biomarkers, in addition to Ki-67, which can all be detected by immunohistochemistry. In situ hybridization techniques are used in equivocal cases for HER2. Ongoing research on a variety of biomarkers, ranging from morphological markers, such as tumor-infiltrating lymphocytes, to mutation profiles, such as altered BRCA1, BRCA2, PIK3CA, TP53, and PALB2, have enabled clinicians to detect underlying genetic alterations, develop novel therapeutic approaches, and predict therapy response in these patients. Nevertheless, in order to improve prognosis and survival of these patients, accurate application and correct evaluation of molecular alterations are crucial.