Biomarkers in Breast Cancer: Where Are We and Where Are We Going?

Biomarkers play an important role in the detection and management of patients with breast cancer. Thus, BRCA1/2 mutation testing is used for risk assessment in families with a high prevalence of breast and ovarian cancer. Following a diagnosis of breast cancer, measurement of multi-analyte profiles such as uPA/PAI-1 or Oncotype DX may be used for determining prognosis and identifying lymph node-negative patients who may be spared from having to receive adjuvant chemotherapy. Other -gene tests such as the PAM50 ROR, Breast Cancer Index, and EndoPredict have been reported to predict the development of late recurrences and thus may be of value in selecting patients for extended hormone therapy. Mandatory assays include estrogen receptors for identification of endocrine-sensitive cancers and HER2 in selecting patients for treatment with anti-HER2 therapy (e.g., trastuzumab, lapatinib, pertuzumab, and ado-trastuzumab emtansine). Finally, serum biomarkers such as CA 15-3 or CEA may be used in monitoring therapy in patients with advanced disease receiving systemic therapy. Promising new biomarkers undergoing evaluation include circulating tumor cells and circulating tumor-derived DNA.