The aim of this trial is to identify biomarkers and genetic predisposition for the development of immune checkpoint related colitis.

Immunotherapy with immune checkpoint-inhibitors is standard treatment for patients with melanoma. However, in about 15% of patients treated with Ipilimumab a grade 3-4 colitis will occur. In programmed cell death protein 1 (PD1) inhibitors colitis is also seen as adverse event, although less prominent. We want to find a good predictive biomarker to select patients that are prone to colitis.So far no test is available that might be predictive whether a patient will develop a grade 3-4 colitis.

The study will consists of four parts: 1.) to identify a genetic profile associated with ipilimumab-induced colitis, 2.) to identify predictive (serum or fecal) biomarkers for ipilimumab-induced colitis, 3.) to study the tissue of ipilimumab-induced colitis and 4) to study the role of the gut microbiome in the development of colitis. Patients are able to participate in one, or more parts of the study.

Inclusion Criteria:

1. Patients with melanoma who will be treated with immune checkpoint inhibitors (ipilimumab, nivolumab, pembrolizumab)
2. Signed written informed consent.
3. Able to comply with the protocol.

Exclusion Criteria:

1. Patients with a pre-existing colitis (e.g. Crohn's disease, ulcerative colitis).

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