Validated biomarkers: The key to precision treatment in patients with breast cancer.

Recent DNA sequencing and gene expression studies have shown that at a molecular level, almost every case of breast cancer is unique and different from other breast cancers. For optimum management therefore, every patient should receive treatment that is guided by the molecular composition of their tumor, i.e., precision treatment. While such a scenario is still some distance into the future, biomarkers are beginning to play an important role in preparing the way for precision treatment. In particular, biomarkers are increasingly being used for predicting patient outcome and informing as to the most appropriate type of systemic therapy to be administered. Mandatory biomarkers for every newly diagnosed case of breast cancer are estrogen receptors and progesterone receptors in selecting patients for endocrine treatment and HER2 for identifying patients likely to benefit from anti-HER2 therapy. Amongst the best validated prognostic biomarker tests are uPA/PAI-1, MammaPrint and Oncotype DX. Although currently, there are no biomarkers available for predicting response to specific forms of chemotherapy, uPA/PAI-1 and Oncotype DX can aid the identification of lymph node-negative patients that are most likely to benefit from adjuvant chemotherapy, in general. In order to accelerate progress towards precision treatment for women with breast cancer, we need additional predictive biomarkers, especially for enhancing the positive predictive value for endocrine and anti-HER2 therapies, as well as biomarkers for predicting response to specific forms of chemotherapy. The ultimate biomarker test for achieving the goal of precision treatment for patients with breast cancer will likely require a combination of gene sequencing and transcriptomic analysis of every patient's tumor.