The inflammatory microenvironment is thought to play a pivotal part in tumorigenesis. But, can the brain be informed about peripheral preclinical cancer cells? Can it modulate tumour development? One of the key routes for information to reach the brain from visceral regions is through the vagus nerve. Yet, patients with ulcers who have had a vagotomy have been shown to die from cancer more frequently than do those who have not had this procedure, and surgical and chemical vagotomy attenuates tumour-induced anorexia and leads to enhanced tumour progression. We therefore postulate that the vagus nerve participates in informing the brain about tumorigenesis by transmiting information to the brain about tumour-associated proinflammatory cytokines. Furthermore, activation of the vagus could slow tumorigenesis by suppression of peripheral proinflammatory cytokines.