Clinical target sequencing for precision medicine of breast cancer.

Precision medicine can be defined as the customization of medical treatment based on the individual genetic profile, which enables one to identify patients who respond to therapies while sparing side effects for those who do not. Breast cancer patients have been treated based on subtyping, which is considered a prototype of precision medicine. Furthermore, the development of multigene panel testing has resulted in a paradigm shift in the treatment of breast cancer. The knowledge generated from the Human Genome Project, and subsequently The Cancer Genome Atlas, has provided the concept of precision medicine, in which cancer patients can be sub-classified based on actionable driver mutations that can be selectively targeted by molecular targeted drugs and treated by appropriate molecular targeted therapies. Development of next-generation sequencing has both dramatically advanced genomic sequencing technology and revealed actionable driver mutations for individual cancer patients when applied to a clinical setting. Clinical target sequencing by next-generation sequencing enables one to formulate treatment strategies, not only by selecting a subgroup of patients who are expected to experience more effectiveness of each drug, but also by revealing patients with drug resistance based on their actionable driver mutations.