Applicability and limitations of a recently-proposed prognostic grading metric, initial brain metastasis velocity, for brain metastasis patients undergoing stereotactic radiosurgery.

Abstract

This study, based on our brain metastasis (BM) patients undergoing stereotactic radiosurgery (SRS) procedures, aimed to validate whether the recently-proposed prognostic grading system, initial brain metastasis velocity (iBMV, scoring the cumulative number of BMs at the time of SRS divided by time [years] since the initial primary cancer diagnosis), is generally applicable. This was an institutional review board-approved, retrospective cohort study using our prospectively accumulated database including 3498 patients who underwent SRS for BMs during the 19.5-year-period between July, 1998 and December, 2017. We excluded four lost to follow-up, 24 for whom the day of primary cancer diagnosis was not available, 665 with synchronous presentation and 651 with pre-SRS radiotherapy and/or surgery, ultimately studying 2150 patients. Patients were categorized into two classes by iBMV scores, i.e., < 2.00 and ≥ 2.00. In a multivariable model, iBMV was directly associated with a higher risk of death (p < 0.0001). The median survival time of patients with iBMV scores < 2.00, 10.0 (95% CI; 9.2-10.9) months, was longer than that of patients with iBMV scores ≥ 2.00, 6.3 (5.6-6.7) months, showing a significant difference between the two groups (HR 1.599, 95% CI 1.458-1.753, p < 0.0001). The same results were obtained in patients with non-small cell lung, breast, kidney or other cancers. Among 608 patients who underwent repeat SRS for newly-developed BMs, iBMV score categories correlated well with brain metastasis velocity risk groups (p < 0.0001). Our present results support the validity of iBMV for predicting survival after SRS.