Local metastatic expansion versus secondary intra-organ dissemination: two causes of neurological death explained by fundamentally different metastatic colonization patterns

Background Neurological failure contributes to 15–50% of deaths in patients with brain metastases, yet the underlying mechanisms remain poorly understood. Clinical causes range from local compression to meningeal metastasis. In this context, a link between infiltrative histopathological growth patterns (HGPs) and meningeal metastasis was recently described and prompted this reverse translation study. Methods We conducted a retrospective postmortem histological assessment and a prospective MRI-based proof-of-concept study to explore neurological decline mechanisms in two experimental brain metastasis models with different HGPs: (i) the non-infiltrative TUBO model, characterized by well-defined tumor borders and a multilayered astrocytic capsule; and (ii) the infiltrative E0771-LG model, exhibiting diffuse infiltration and widespread astrogliosis. Results In the TUBO model, neurological death resulted from local metastatic expansion compressing vital structures, while the E0771-LG model caused mortality mainly through widespread secondary dissemination. We provide the first direct evidence of contralateral recolonization by secondary metastasis-initiating cells (secMICs), and highlight the high efficiency of secondary spread. Additionally, we show that secMICs exploit distinct anatomical structures to reach distant brain regions, bypassing classical vascular dissemination routes. Notably, the HGP and its associated features are intrinsic to tumor cells and are established early during metastatic colonization. Conclusions This study identifies the HGP as a potential surrogate for predicting the underlying cause of organ failure in brain metastases. Additionally, it highlights the significant role of secondary dissemination and recolonization in brain metastasis, processes that have been largely overlooked in clinical practice. These findings address a critical knowledge gap and may inform future treatment strategies.