Progress in targeted therapy for breast cancer

Breast cancer is a multistep, multifactorial, and heterogeneous disease. Significant transformations have occurred in the systemic management of breast cancer in the past decade. Due to the further understanding of pathogenesis, scientists have found plenty of signaling pathways and correspondingly therapeutic targets in breast cancer, such as hormone receptor, human epidermal growth factor receptor 2 (HER2), epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF), phosphoinositide-3-kinase (PI3K), v-akt murine thymoma viral oncogene homolog (AKT), mechanistic target of rapamycin (mTOR), cyclin-dependent kinase 4/6 (CDK4/6), poly (adenosine diphosphate-ribose) polymerase (PARP), and programmed death-1 (PD-1). Targeted therapy, which optimizes the accuracy of antitumor activity and minimizes toxicity to normal tissues, plays a crucial role in breast cancer treatment in the era of precision medicine. In this review, we aimed to summarize the latest developments in targeted therapy for breast cancer and discuss the existing problems.