How Does Brainstem Involvement Affect Prognosis in Patients with Limited Brain Metastases? Results of a Matched-Cohort Analysis

Objective: Although brainstem metastases are thought to portend an inferior prognosis compared to non-brainstem brain metastases, there is limited evidence to support this claim, particularly in the modern radiosurgical era. Methods: We collected the clinical data for 500 patients with brain metastases treated at our institution with stereotactic radiosurgery (SRS). All patients received SRS to at least one brain metastasis, and all brainstem metastases underwent SRS. After propensity score matching, clinical characteristics and overall survival were calculated and compared between groups. Results: Three hundred sixteen patients with brain metastases were analyzed after matching (143 with brainstem involvement and 173 without). Patients with brainstem metastases lived shorter after first SRS than patients without brainstem metastases did (median 4.4 and 6.5 months, respectively; P = 0.01), and they were more likely to have received whole brain irradiation (P = 0.003). Patients with a single metastasis did not survive longer than patients with multiple brain metastases if there was brainstem involvement (P = 0.45). The incidence of new extracranial disease and severe toxicity after SRS did not differ between groups. Conclusions: The survival of patients with brain metastases is inferior after a metastatic lesion develops within the brainstem, despite favorable local control with brainstem SRS. The brainstem location should be considered a negative prognostic factor for survival after SRS, and it could result from the eloquence of this location. Future research could identify the clinically life-limiting component of brainstem metastases.