<p>The mammalian polyamines (putrescine, spermidine and spermine) are ubiquitous polycations, long recognized for their indispensable roles in maintaining cell proliferation, differentiation and survival. Traditionally viewed as metabolic supporters of growth, polyamines have recently emerged as active regulators of cell-cell signaling in diverse physiological and pathological settings. Through intercellular polyamine transfer, modulation of ion channels and interactions with cell-surface receptors, polyamines orchestrate intricate signaling networks, from neurotransmission in the nervous system to cytokine signaling in the immune compartment. Many cancers, though most clearly, central nervous systems (CNS) cancers, exploit neuro- and immunomodulatory circuits, effectively hijacking neural and immune signaling pathways to sustain growth and evade surveillance. Thus, an integrated, multi-disciplinary perspective is required to overcome hurdles in the treatment of these aggressive malignancies. In light of ongoing clinical trials aimed at disrupting polyamine synthesis and transport in brain tumors, better defining the role of polyamines in mediating tumor-host interactions is essential for maximizing anti-tumor efficacy while minimizing normal tissue toxicity. This review integrates advances from cancer biology, immunology and neuroscience to comprehensively discuss the mechanisms through which polyamines regulate cell-cell signaling, the role of these pathways in brain tumor progression and the diagnostic and therapeutic opportunities that arise from this knowledge.</p>