Top Line: Where are we with metastasis-directed therapy for oligometastatic breast cancer?
The Study: Patients with metastatic breast cancer have some of the longest survival times in oncology, yet they are not often the center of discussions about metastasis directed therapy for oligometastatic disease. Here is a systematic review and meta-analysis of studies using SBRT for oligometastatic breast cancer. Eligible studies treated patients with ≤ 5 metastasis using ≥ 5 Gy per fraction with ≤ 10 fractions. A total of 10 studies were included including 3 prospective trials and 467 patients with 653 metastases. Local control at 1 and 2 years was 97% and 90%, and hormone receptor positivity was associated with better LC. Progression free survival at 1 and 2 years was 63% and 46%. Overall survival at 1 and 2 years was a whopping 93% and 81%, and bone-only disease was associated with better OS. Only a few trials reported outcomes according to both hormone receptor and HER2 receptor status with HER2+ and HR+/HER2- having survival far superior to oligometastatic TNBC (32% at 2 years). The rate of grade 3+ toxicity was < 1% with no grade 4 or 5 events. Of note, some trials only included patients with ≤ 3 oligometastases, however there was no difference in local control or survival compared to patients with 4-5 mets. Unfortunately, there was significant heterogeneity in radiation regimens ranging from 20 Gy in 1 fraction to 75 Gy in 3 fractions to 50 Gy in 10 fractions. BED(10) ranged from 60 to 262 Gy, and the median BED(10) was 75 Gy.
Top Line: Select patients who are eligible for metastasis-directed therapy for oligometastatic breast cancer have excellent local control and very low toxicity with SBRT, but we need randomized data to determine whether this changes disease trajectory. | Viani, Radiother Oncol 2021