Metastatic brain tumors, which include both primary metastatic disease that initiated within the central nervous system (CNS) and secondary metastatic disease that started systemically and metastasized to the CNS, are collectively the most prevalent types of intracranial tumor.[1] Standardized treatment including surgery followed by either focal or whole-brain radiation have allowed for excellent local control rates.[2,3] In the setting of neurological complications related to these tumors, much work has been done to understand the key markers of prognostic and predictive significance. In addition, improved mortality rates in cancer patients have come at the cost of increasingly complicated treatment regimens including cytotoxic, immunological, surgical, and radiation-based therapies. Underlying heterogeneity across different types of metastatic brain disease is a contributing factor to this challenging decision-making process. In addition, only the presence or absence of brain metastasis at the time of initial diagnosis is noted in many historical studies, decreasing the overall detection of metastatic brain disease that develops later in the disease course.