Modelling Brain Metastasis: Standardized Analysis of Metastatic Colonization and Histological Growth Patterns by Stereotactic Intracortical Injection

Brain metastases are a common and devastating complication of advanced solid tumors, frequently associated with poor prognosis, neurological decline, and reduced quality of life. The incidence of central nervous system (CNS) failure and neurological death is rapidly increasing, yet the mechanisms driving the final stages of brain metastasis, such as secondary dissemination, re-colonization, and the contribution of the histological growth pattern (HGP) as a potential surrogate parameter, remain poorly understood. The standardized stereotactic intracortical injection model enables precise and reproducible implantation of tumor cells, or mixed populations including stromal or immune components, directly into the mouse cerebral cortex. This protocol also supports the creation of a preclinical tissue archive, offering a robust platform for investigating essential aspects of CNS colonization, such as: metastatic outgrowth, HGP-specific growth dynamics, and pathophysiological mechanisms contributing to neurological failure. Additionally, this model supports pharmacological testing in a reproducible clinically relevant context. Unlike systemic injection methods (e.g., tail vein or intracardiac), which are optimized for studying early metastatic steps but result in variable and often low rates of brain colonization, the stereotactic model ensures consistent, brain-specific metastatic growth and enables the investigation of late stages of CNS metastasis. Compared to ex vivo systems such as organoids or brain slice cultures, the in vivo stereotactic model preserves vascularization, systemic signaling, and the full complexity of the brain's immune landscape, supporting long-term studies of tumor progression and therapeutic response. By providing a reproducible and clinically relevant platform, our model advances the field's ability to identify prognostic markers, explore therapeutic strategies, and understand the mechanisms of late-stage brain metastasis.