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.