In this study, mucosal biopsies were collected from the lesions and the underlying fistulous tracts, which showed granulomatous tissue infiltrated by mucus-producing adenocarcinoma. The study proved that the constant mucosal regeneration inside a fistula in Crohn’s disease tends to be a common pathogenetic mechanism for developing carcinoma. At the same time, immunosuppressants and anti-TNF agents may also lead to the malignant transformation. This evidence concerns the gene TNF and Crohn disease.