9. Liquid Biopsy in Breast Cancer

Breast cancer (BC) to date remains the most common cancer in women. Nowadays, BC is often diagnosed at local disease stage, and, after surgery, based on individual’s risk of relapse, the patients undergo adjuvant systemic treatment to decrease the risk of recurrence. Current BC classification and assessment remain strongly based on clinicopathological criteria, including patient age, tumor size, lymph node invasion, histological type, and grade. According to standard practice, the choice of treatment strategy includes assays for estrogen (ER) and progesterone (PgR) receptor expression levels, overexpression of human epidermal growth factor receptor 2 (Her-2), or amplification status of the correlate oncogene, but also histological grade and Ki67 to evaluate proliferation of tumor cells. Nevertheless, the established clinicopathological parameters are not sufficient anymore for clinical decision-making and should be combined with genomic profiling to estimate recurrence risk and identify high-risk BC patients (prognostic value) and predict optimal treatment for each disease subgroup (predictive value). The information obtained from standard tumor tissue sampling cannot be the same for the whole tumor and offer a static picture of disease. The constant molecular change of tumor cell population, spatial and temporal, requires a noninvasive approach, for real-time picture of disease. Liquid biopsy is a useful tool to follow the continuously evolving genomic landscape of breast cancer.