Preclinical data have shown that neurotransmitters released in peripheral tissues from nerve endings may influence carcinogenesis, affect the tumor microenvironment, and directly potentiate both proliferation and migration of cancer cells. This stimulatory role of the nervous system in cancer initiation and progression has also been documented by clinical studies investigating the effect of attenuated signaling from nerves innervating cancer tissue. However, compared to preclinical studies, clinical studies are rarer and some of them have ambiguous results. In this retrospective analysis, to assess the effect of the nervous system on cancer, we analyzed published clinical studies investigating the incidence of cancer in patients with spinal cord injury or pheochromocytoma. Our findings support a concept of the neurobiology of cancer based on the assumption that the nervous system affects cancer initiation and progression (Ref. 60). Keywords: cancer, neurobiology of cancer, norepinephrine, sympathetic nervous system, spinal cord injury, pheochromocytoma.