In the present study, we therefore analyzed the expression of ectopic MUC5AC in the mucous cells of the large and small intestines in patients with CD undergoing ADA treatment as the first TNF-α inhibitor (cases naïve to anti-TNF treatment) before and at 12 and 52 weeks after the start of ADA therapy, using C-reactive protein (CRP), the CD activity index (CDAI), and CD endoscopic index of severity (CDEIS) scores as a measure of disease activity, retrospectively. The gene discussed is MUC5AC; the disease is Cowden disease.