Distinct tumor architectures for metastatic colonization of the brain [scRNA-seq]

Brain metastasis is a dismal complication of cancer that hinges on the initial survival and outgrowth of disseminated cancer cells. To better understand these crucial early stages of brain metastatic colonization, we investigated two prevalent sources of cerebral relapse in the clinic, triple-negative breast cancer (TNBC) and HER2+ breast cancer (HER2BC). We elucidated distinctive early tumor architectures, physical and functional stromal interfaces, and autocrine growth programs employed by these two tumor types to colonize the brain. TNBC cells form extensive perivascular sheath colonies with diffusive contact with astrocytes and microglia. In striking contrast, heightened autonomous deposition of several extracellular matrix components prompts HER2BC cells to colonize the brain as compact, spheroidal colonies, segregating stromal cells to the periphery of the colony. Single-cell dissection of the spatially resolved tumor microenvironment (TME) reveals that brain metastases activate – to different degrees – the canonical stages of the disease-associated microglia (DAM) response previously defined in Alzheimer’s disease. Differential engagement of paracrine tumor-DAM signaling through the receptor AXL suggests specific pro-metastatic functions of the tumor architecture in both TNBC perivascular and HER2BC spheroidal colonies. Collectively, our findings illuminate the distinct stereospatial features of two different yet highly efficient modes of brain colonization, and the relevance of these features in future efforts to leverage the TME to treat brain metastasis. Xenograph model mice were injected with MDA231-BrM or HCC1954-BrM cells and brains were harvested after 30 days of growth for scRNA-seq. Additional processed data files required to run the code uploaded to GitHub (https://github.com/dpeerlab/Brain-metastasis-TME) are deposited in Zenodo (https://doi.org/10.5281/zenodo.13863738).