Brain metastases (BM) are the most prevalent tumors of the central nervous system (CNS), with a ratio of 10: 1 relative to primary tumors. In breast cancer, BM are becoming more frequent due to longer life expectancy. Patients with HER2-positive metastatic disease are prone to develop BM more often and they occur in 20 - 40% of cases. Circulating tumor cells (CTC) originate from the primary tumor and can migrate to distant organs. The possible correlation between CTC and the incidence of brain metastases could help define radiotherapy in patients with oligometastatic or not so widespread disease in the brain. However, there are few studies that evaluate these scenarios. Purpose: To assess the number of CTC before and 4-5 weeks after focal stereotactic radiotherapy in single (SRS) or fractionated (SFRT) dose and correlate with the local and distant brain progression free survival in patients with metastatic breast cancer. Potential invasion markers in these cells will be evaluated and correlated with clinical outcome. Patients and Methods: Prospective, single-center research which will be developed at the Radiation Oncology Department of AC Camargo Cancer Center. Patients with diagnosis of metastatic breast cancer to the brain with an indication of focal radiotherapy, SRS or SFRT, will be recruited. The blood will be collected and processed for analysis of CTC by the ISET method (Rarecells, France). The invasion markers (HER-2, COX-2, EGFR, Notch 1 and ST6GALNAC5) will be analyzed on CTC by immunocytochemistry. Expected Results: If our hypothesis is proven, we may include the analysis and quantification of CTC in clinical practice as early indicator of local or distant recurrence in the brain.
