This is an observational case-control study which enroll metastatic and non-metastatic colorectal cancer (CRC) patients. The objective of this study is to evaluate a novel blood multi-marker test for the detection of relapse in colorectal cancer patients. This test is based on whole-blood transcriptomic signatures and circulating tumor methylated DNA markers. The patients will be enrolled into 4 study groups, two cross-sectional and two longitudinal groups, to follow up patients up to 36 months from primary tumor resection.

Inclusion Criteria:

• Male or female ≥ 18 years of age at time of informed consent.
• Subject has signed the informed consent form (ICF) and is able to understand the information provided in it.
• At least a blood sample is collected per subject according to the sample collection protocol.
• Patients enrolled in local prospective protocols, in which samples have been collected according the study procedures may be included.
• Group 1: patients with a radiologically and, whenever is possible, histologically confirmed relapse (local or distant) of colorectal cancer within 5 years from primary surgery. Metachronous primary tumors are not considered as relapse and should be excluded.
• Group 2: Patients declared disease-free for at least 36 months but less than 5 years, as confirmed by radiological examination.
• Group 3: Patients with a stage III-IV colorectal cancer with a curative treatment and disease-free for at least 3 months but less than 18 months.
• Group 4: Histologically and radiologically confirmed diagnosis of stage I, II, III or IV colorectal adenocarcinoma, eligible for a treatment with curative intent.

Exclusion Criteria:

• Personal history of cancer (non-hematologic) other than CRC in complete remission for less than 5 years.
• Personal history of hematologic cancer.
• A blood transfusion within 6 weeks prior to inclusion into the study.
• Transplant with regular intake of immunosuppressants.
• Pregnant woman (self-declaration).
• Conditions or comorbidities that would preclude the compliance with the planned surveillance program or with the protocol as judged by the Investigator.
• Previous inclusion in the RELMA-C study and/or re-inclusion in a different study group.
• Group 1: Any treatment for CRC relapse prior to blood collection.
• Group 2: Patient is disease-free for less than 36 months or more than 5 years.
• Group 3: Patient is disease-free for less than 3 months or more than 18 months
• Group 3: Stage IV patients with detectable residual disease after primary treatment.
• Group 4: Any cancer treatment prior to blood collection.

The study will enroll CRC patients into 4 study groups. G1: patients with an actual diagnosis of CRC relapse. G2: patients declared disease-free for at least 36 months but less than 5 years.

G3: stage III-IV CRC patients who underwent a curative treatment and are disease-free after primary treatment for more than 3 but less than 18 months.

G4: patients diagnosed with primary CRC without any cancer treatment.