Follow-up study of liver metastasis from breast cancer treated by proton beam therapy.

Liver metastasis from breast cancer (LMBC) is an incurable, fatal disease with a very poor prognosis. Although various local treatments have been applied, their clinical utility has not been established. The purpose of this study was to investigate the safety and effectiveness of proton beam therapy (PBT) for the treatment of patients with LMGC. A total of 8 female patients (aged 38-63 years) with LMBC who received PBT between 2002 and 2012 were retrospectively reviewed. Patients who had tumors confined to the liver were investigated, whereas patients with extrahepatic tumors were excluded. A total of 5 patients had solitary tumors and 3 had multiple tumors. The total irradiation dose was 66-72.6 Gray equivalent [Gy relative biological effectiveness (RBE)] and 2 patients received concurrent chemotherapy or hormone therapy. The overall and progression-free survival (OS and PFS) rates, local control (LC) rate and adverse effects were investigated. All the patients completed treatment without interruption and late adverse effects of grade >3 were not observed. The OS rate was 88/73/58%, the PFS rate was 50/25/0% and the LC rate was 86/86/86% at 1/3/5 years, respectively. Thus, PBT is a safe treatment and the OS and PFS rates are comparable to those with other local treatments. PBT may be considered as an effective local treatment option for the treatment of LMBC patients.