Spatial analysis of the metastatic brain tumor immune and extracellular matrix microenvironment

Metastatic cancer is responsible for the overwhelming majority of cancer-related deaths, with metastatic tumors being the most common neoplasms affecting the central nervous system. One of the major factors regulating tumor biology is the tumor microenvironment. However, little is known about the cellular and non-cellular composition of metastatic brain tumors and how tumor cell ontogeny influences the metastatic brain tumor microenvironment. By integrating multiplex immunohistochemistry and histopathological analysis to investigate composition and the spatial relationship between neoplastic cells, infiltrating and brain resident immune cells and the extracellular matrix, we demonstrate that metastatic brain tumors exhibit differences in extracellular matrix deposition, compared with the most common primary brain tumor type, glioblastoma, and that the dominant immune cell types in metastatic brain tumors are immunosuppressive macrophages, which preferentially localize to extracellular matrix-rich stromal regions.