An increasing number of patients with metastatic colorectal cancer (mCRC) are able to receive 3 or more lines of therapy. In this setting, can be recognize treatments such as regorafenib (an oral multikinase inhibitor), trifluridine/tipiracil hydrochloride (TAS-102), an antineoplastic nucleoside analogue, and antibodies anti-epidermal growth factor receptor (EGFR) in patients with RAS wild-type tumors (if no prior exposure to antibodies). Maintaining quality of life is an essential goal for third- and later-line treatments for patients.

The anti-programmed cell death protein 1 (anti-PD-1) immune checkpoint inhibitors, pembrolizumab and nivolumab, were approved in the US by the FDA in 2017, and the combination nivolumab plus ipilimumab (anti CTLA-4) was recently approved by the FDA in 2018, all in the second and later-line setting for patients with microsatellite instability-high (MSI-H) or deficient DNA mismatch repair mCRC whose disease has progressed despite treatment with fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy. At present, these agents are not approved in Europe for mCRC patients with MSI-H. Clinical trial results and scientific data supported evidence that immunotherapies provide benefit but are limited to the small proportion (< 5%) of patients with MSI-H tumors, in whom they are highly effective. Therefore, patients with MSI-H disease should be referred as expeditiously as possible to receive immune checkpoint inhibitors.

The aim the study is to retrospectively collect data of patients treated with immunotherapy in the context of real clinical practice, in order to describe the real impact in terms of clinical outcomes and tolerability of treatment in common clinical practice.

Inclusion Criteria:

• Signed informed consent for alive patients
• Patients with diagnosis of colorectal cancer with MSI-H
• Patient treated with at least one administration of antibody anti PD-1 for colorectal cancer prior to 30 June 2020 outside clinical trials.
• Availability of the tumor tissue from the primary tumor or a metastatic site for molecular analyses. The availability of tumor tissue is recommended but not mandatory.

Exclusion Criteria:

• Patients who received immunotherapy during a clinical trial.

Patients with colorectal cancer treated with at least one administration of immunotherapy prior to 30 June 2020