Circulating tumor cells in breast cancer: methodology and clinical repercussions.

Breast cancer is the most common type of cancer among women, and clinicians have long recognized its heterogeneity. Its detection and treatment in early stages allow for reduction of mortality. Despite the advances and new strategies for combining surgical, radiotherapy, and chemotherapy options, however, the percentage of patients developing metastases and advanced stages remains high. Even though serum tumor markers have been used for the early diagnosis of metastases, their systematic determination has not had an effect on survival. Methods that are more reliable are needed to detect metastases earlier than with the common clinical methods and thus start treatment before overt relapse. Early indicators of response or resistance to treatment are also an issue in clinical practice. Imaging techniques are time consuming, and it is difficult to detect changes that indicate response limited to therapy, and approaches to defining changes in tumor mass are time and resource consuming. In contrast, detection of circulating tumor cells (CTC) could be a useful tool in early detection of relapse and response to systemic chemotherapy. Extremely sensitive techniques are available that are easily applied to peripheral blood samples, which might provide enormous research possibilities in this area.