Both ulcerative colitis and Crohn's colitis are associated with an increased risk of developing colorectal cancer (CRC). Although the increased risk of CRC in colitis patients is well established, several studies show that the risk varies widely between patients, depending on the presence of risk factors. Recently, several of these risk factors were implemented in the updated British guidelines for surveillance which are now used to determine surveillance intervals in our center. The new guideline recommends stratification of patients in a high, medium or low risk group depending on the presence of clinical and endoscopic risk factors and to adjust the surveillance interval accordingly. Although these guidelines provide a first step towards an individualized surveillance regimen, current data regarding risk factors for IBD (inflammatory bowel disease) -associated CRC are solely based on retrospective studies. Prospective data on the phenotype and genotype reliably predicting the risk of CRC is needed to further optimize surveillance in the future.

Objectives:

1. To confirm established and identify new predictive factors for colorectal cancer in a prospective cohort of IBD patients undergoing regular surveillance. Dysplasia or colorectal cancer will be the primary outcome.
2. To provide evidence that mucosal healing results in a significant reduction of colorectal dysplasia/neoplasia in IBD patients and that this is associated with 5-ASA (5-aminosalicylic acid) or anti-TNF (tumor necrosis factor) maintenance therapy.
3. Study the expression of several tumor markers in biopsies, blood and faeces at baseline and determine whether expression of these markers can predict dysplasia or colorectal cancer development during follow-up.

Inclusion Criteria:

• Diagnosis of ulcerative colitis, crohn's colitis or indeterminate colitis
• Disease duration ≥ 8 years
• Inflammation of at least 30% of colonic mucosa at some point between IBD diagnosis and inclusion
• Age 18 - 70 years
• Signed informed consent

Exclusion Criteria:

• High grade dysplasia or colorectal cancer before inclusion
• subtotal or total colectomy before inclusion
• Clotting disorder or use of anticoagulants that can not be temporarily discontinued
• Serious comorbidities which prevent performing a colonoscopy
• Limited life expectancy
• Clinical or endoscopical disease activity (at the discretion of the treating physician)

patients with a diagnosis of ulcerative colitis, Crohn's colitis or indeterminate colitis between 18 and 70 years of age. Patients should have an indication for surveillance according to the current guidelines, which means a disease duration of at least 8 years and involvement of at least 30% of the colon.