Gut microbiota in brain tumors: An emerging crucial player

In recent decades, various roles of the gut microbiota in physiological and pathological conditions have been uncovered. Among the many interacting pathways between the host and gut flora, the gut–brain axis has drawn increasing attention and is generally considered a promising way to understand and treat brain tumors, one of the most lethal neoplasms. In this narrative review, we aimed to unveil and dissect the sophisticated mechanisms by which the gut‐brain axis exerts its influence on brain tumors. Furthermore, we summarized the latest research regarding the gastrointestinal microbial landscape and the effect of gut–brain axis malfunction on different brain tumors. Finally, we outlined the ongoing developing approaches of microbial manipulation and their corresponding research related to neuro‐malignancies. Collectively, we recapitulated the advances in gut microbial alterations along with their potential interactive mechanisms in brain tumors and encouraged increased efforts in this area. Gut microbiota is a crucial component of the gut–brain axis. Perturbations in gut microbiota composition may set fire to the development of brain tumors. Here in this review, gut–brain axis was classified into three pairs of interactions, including immunological modulation, microbial metabolites‐mediated modulation, and direct invasion. By regulating the secretion of inflammatory factors and immune cell‐mediated responses, microbiota, and tumor cells interact with each other distantly. Microbial metabolites could be transported from gut to the brain via circulation, and thus intestinal metabolic imbalance might augment the overall metabolic imbalance seen in brain tumors. Apart from microbe‐related metabolites, microbe itself could be transported directly through BBB breach via circulation or parasitized immune cells. Specifically, we illustrated the altered microbial landscapes of three most common brain tumors (glioma, meningioma, and pituitary adenoma) along with their potential connections with disease‐specific pathological process.