This is a multicentric, observational study, including all European centres willing to take part. The multicentre nature is necessary for enhancing the generalisability of our results, and due to the rarity of this condition. The study is observational including both retrospective and newly diagnosed cases of CIC with an endoscopically/histologically-proven diagnosis. Detailed characteristics will be collected, with the aim of classifying the disorders from a clinical, endoscopic, and pathological point of view. Age, sex, localisation, and histology of tumour, stage of tumour, oncological response to immune checkpoint inhibitors-induced colitis, colonoscopy, histology, inflammatory parameters, and clinical manifestations will be assessed for each patient, as well as therapy and outcome.

The study will consist of 2 part: the first one will be retrospective, while the second one will be prospective al will include all incident patients diagnosed with CIC during the enrolment period.

Inclusion Criteria:

• age ≥ 18 years;
• patients able to provide informed consent or who have already given leave of use of their data for research in the retrospective part; waiving of the informed consent may be applied if national regulations allow to do so;
• patients who have undergone at least one cycle of immune checkpoint inhibitors before the onset of intestinal symptoms;
• patients with at least one colonoscopy showing macroscopical and/or histological colitis after commencement of immune checkpoint inhibitors therapy; for retrospective patients only, a follow-up of at least 12 months, unless death occurred before.

Exclusion Criteria:

• Evidence of colitis/inflammatory bowel disease prior to checkpoint inhibitors administration

Patients with a histologically proven CIC or enterocolitis. Any cancer patient who is started on any available immune check-point inhibitor and developing CIC/enterocolitis will be enrolled.