Objective Neuroendocrine tumor is a nervous system disease that threatens the life of patients. The decline of immunity in patients with neuroendocrine tumors is one of the causes of the deterioration of the tumor. The relationship between neuroendocrine tumor and immune molecule MAVS remains to be studied. Methods 468 patients with neuroendocrine tumors were admitted to hospital as the research object (including 161 cases of neuroendocrine tumors and 207 patients with severe neuroendocrine cancer patients), and 207 healthy volunteers were considered as control. Protein levels of MAVS in blood cells of neuroendocrine cancer patients and healthy volunteers were measured by western blot assay before and after treatment. The correlation between the levels of MAVS and the neuroendocrine tumor was analyzed. Results The protein levels of MAVS in the blood cells of neuroendocrine cancer patients were significantly higher than that in the healthy volunteers (P<0.05). The expression of MAVS in the blood cells of neuroendocrine cancer patients was decreased after treatment. Protein levels of MAVS in the blood cells of severe neuroendocrine cancer patients were significantly higher than that of patients with general neuroendocrine tumor (P<0.05). The MAVS in the blood cells is positively correlated with the degree of deterioration of neuroendocrine tumors. Conclusion The MAVS in the blood cells could be a specific biomarker for neuroendocrine tumor diagnosis. The levels of MAVS were positively correlated with the degree of deterioration of neuroendocrine tumors.