Oligometastatic Breast Cancer Patients Treated with High-Dose Chemotherapy and Targeted Radiation: Long-Term Follow-Up of a Phase II Trial

SIMPLE SUMMARY: Based on recent clinical trials, radiation is a standard treatment option for limited metastatic sites in metastatic breast cancer, with the potential to improve survival. This is typically given in the form of high-dose radiation called stereotactic body radiotherapy (SBRT). However, SBRT is a newer technology that is not on option for all patients and does not have long-term follow-up. Prior to the widespread implementation of SBRT, we performed a clinical trial utilizing high-dose chemotherapy and standard radiation for metastases in patients with limited metastatic breast cancer. In this research, we analyzed the long-term outcomes of these patients. We found that, despite not using SBRT, radiation provided promising long-term disease control and survival. Therefore, conventional radiation might still be considered if SBRT in not an option for a patient, and our results also help suggest what long-term outcomes of SBRT treatment might look like. ABSTRACT: Background: Patients with oligometastatic breast cancer (oMBC) may benefit from aggressive local therapy. We sought to assess the effects of consolidative radiation therapy (RT) on outcomes in oMBC patients treated on a prospective phase II trial of high-dose chemotherapy (HDCT). Methods: Between 2005 and 2009, 12 patients with oMBC (≤3 metastatic sites) cancer were treated on protocol. Patients were to receive tandem HDCT supported by hematopoietic cell rescue (HCR). All radiographically identifiable oligometastatic sites received targeted radiation. Results: HDCT was initiated at a median of 6.7 (3.5–12.7) months after diagnosis of oMBC. Hormone receptors (HR) were positive in 91.6% of patients, and HER2 was overexpressed in 25% of patients. Median radiation dose (EQD2) was 41.2 (37.9–48.7) Gy. Median follow-up was 13.1 (6.8–15.1) years for living patients. Ten-year PFS and OS were 33% (95%CI, 10–59%) and 55% (95%CI, 22–79%), respectively. Durable local control of treated lesions was 87.5%. At the last follow up, two patients remained progression free and two more were without evidence of disease following additional salvage treatment. Conclusions: Although modern systemic therapies have obviated the use of HDC, aggressive local therapy warrants further evaluation and fractionated radiotherapy is a viable alternative if SBRT is not available.