Clinical implementation of biomarkers and signaling pathway as novel targeted therapeutics in breast cancer

Breast cancer (BC) is the most common cancer worldwide, it is highly heterogeneous in nature and is correlated with many risk factors and genetic predisposition. BC is influenced by several parameters and treatment strategies for BC vary by molecular features, including activation or amplification of various biomarkers like estrogen, progesterone and HER2 receptors. Based on mRNA gene expression levels, BC can be divided into molecular subtypes (Luminal A, Luminal B, HER2-enriched, and basal-like). The molecular subtypes provide insights into new treatment strategies and patient stratifications that impact the management of BC patients. For Estrogen-positive early BC, endocrine therapy is recommended while targeted drugs or immune checkpoint blockers are the standard of care for most early-stage HER2-positive BC and triple-negative breast cancer (TNBC) therapy. A greater understanding of the underlying biology of molecular signaling pathways and epigenetic changes during BC transformation have resulted in the development of targeted therapy for breast cancer. This chapter reviews the etiology, histology and classification of BC. We further aimed to summarize and update the current and past knowledge about the molecular/prognostic markers and available treatment options.