The aim of this study is to test Eicosapentaenoic acid's effects on markers relevant to colorectal carcinogenesis, RNA and DNA profiles, and the possibility that Eicosapentaenoic Acid treatment might be associated with changes of the gut microbiota and metabolomic profiles in patients with long-standing ulcerative colitis.

Arm: experimental

Inclusion Criteria:

• Patients with ulcerative colitis (diagnosed based on clinical criteria, endoscopic and histological) lasting over 8 years, with no clinical activity (SCCAI = 0), and in stable treatment (without any change in treatment in the previous 3 months) with mesalamine, immunomodulators and / or biologics.
• Baseline fecal calprotectin> 150 micrograms / g.
• Signed informed consent.

Exclusion Criteria:

• Patients receiving systemic steroids in the two months prior to study entry.
• Patients taking concomitant warfarin or other blood thinners.
• Known or suspected hypersensitivity to eicosapentaenoic acid/omega 3.
• Women who are pregnant or of childbearing age who do not accept the use of contraceptive methods specified in the study (oral contraception, IUDs) and breastfeeding women.
• Patients with severe medical conditions that, in the opinion of the investigator, contraindicate the patient's participation in the study.
• Changes of treatments and / or use of experimental drugs within 3 months before inclusion in the study.
• Use of Probiotics

Arm: no intervention

Inclusion criteria

• Subjects undergoing screening colonoscopy within the regional colorectal cancer screening programme
• Signed informed consent
• Polypectomy with biopsy forceps.

Exclusion criteria

• HBV-positive, HCV-positive, HIV-positive or otherwise affected by infectious diseases
• Subjects undergoing chemo and radiation therapy within six months prior to surgery
• Patients receiving systemic steroid in the two months prior to study entry
• Patients undergoing antibiotic therapy within three months prior to the study
• Patients treated with probiotics