Concurrent systemic treatment during stereotactic radiosurgery for breast cancer brain metastasis: analysis of survival outcomes and propensity score matching analysis

Background: Stereotactic radiosurgery (SRS) has a fundamental role in the treatment of breast cancer brain metastases (BCBM). Current data on the matter comes from trials with brain metastases from any histology or with limited description on survival, focusing mostly on response rate. This retrospective study will assess the impact of SRS on survival and its interaction with systemic treatment (ST). Materials and methods: Charts from January 2011 to July 2022 were retrospectively assessed to investigate the relation between SRS and concurrent ST for BCBM. Since different protocols for ST can be offered, we divided our cohort and assessed the impact of different concurrent ST, in each subtype, on oncological survival outcomes. Results: There were 208 patients, 138 met inclusion criteria. Median follow-up was 10.7 months. Median overall survival (OS), progression-free survival (PFS), survival-free from CNS progression and survival-free from new neurological deficits were 12.5, 14.1, 16.2, and 16.3 months, respectively. For the whole cohort, any concurrent ST did not impact OS (p = 0.68). For hormone-positive patients, concurrent hormone therapy (HT) did not impact OS (p = 0.75). For those receiving anti-human epidermal growth factor receptor-type 2 (anti-HER-2) therapy there was no impact on OS (p = 0.47). Propensity score match analysis found that ST during SRS would reduce the chance of death by 19.4%. ST did not impact toxicities, chances of radionecrosis nor survival free of neurological symptoms. Conclusion: There has been an increase in research on the synergy between SRS and ST. In our study, this synergy was not sensible for oncological outcomes. New prospective research should focus more on survival outcomes than response rate.