Impact of systemic therapy after stereotactic radiosurgery in patients with limited brain-only metastasis

The impact of systemic therapy (ST) on outcomes for patients with brain-only metastases (BrM) in the absence of extracranial disease (ECD) is not well established. We compared outcomes between patients with BrM treated with stereotactic radiosurgery (SRS) who received ST ≤3 months (mos), >3 mos, or not at all after SRS.

We identified BrM patients who completed SRS across two institutions from 1/2015 to 12/2020. Intracranial progression after SRS was determined by brain MRI radiographic recurrence. Overall survival (OS) and intracranial progression free survival (iPFS) estimates were also generated.

In total, 342 patients with BrM were identified. Primary sites included lung (73%), breast (12%), and additional sites (15%). Almost half, 169 (49%), received no ST, 80 (23%) received ST ≤3 mos, and 93 (27%) received ST >3 mos after SRS. Median age was younger in the ST >3 mos cohort (60.5years) compared with ST <3mo (67.7years) and no ST (67.0years), P = .0002. Median OS differed significantly between groups: ST ≤3 mos with 24.9mos (95%CI: 16.6-51.1), ST >3 mos with 27.5mos (95% CI: 20.6-37.5), and no ST with 11.0mos (95%CI: 9-17.5), P = .002. Median iPFS differed significantly between groups: ST ≤3 mos 16.1mos (95% CI: 9.5-33.7), ST >3 mos 8.9mos (95% CI: 6.9-13.5), and no ST 10.0mos (95% CI: 6.7- 15.1). However, timing of ST was not significant multivariate analysis.

In our cohort of BrM patients, ST after SRS improves OS regardless of timing. ST ≤3 mos may improve iPFS compared with ST >3 mos after SRS, which warrants further investigation. Appropriate patients with BrM should be referred for a multi-disciplinary discussion of ST following SRS.