C-reactive protein (CRP) produced locally within esophageal cancer is associated with the prognosis and the rate of recurrence. CRP genetic polymorphisms reportedly affect serum CRP concentrations; however, there are no reports of an association between genetic polymorphisms and tumoral CRP expression. This study enrolled 73 Japanese patients classified with Stage IIA-IV thoracic esophageal squamous cell cancer, and also investigated their CRP genetic polymorphisms using DNA extracted from their peripheral blood. The study then assessed the association between CRP genetic polymorphisms and tumoral CRP expression. The results revealed a significant association between the CRP 1846C>T genetic polymorphism and tumoral CRP expression. This finding suggests that tumoral CRP production controlled by CRP genetics significantly influences tumor behavior.