IMPROVE Intervention Trial Implementing Non-invasive Circulating Tumor DNA Analysis to Optimize the Operative and Postoperative Treatment for Patients With Colorectal Cancer

Inclusion Criteria: * Surgically removed Adenocarcinoma of the colon or rectum * Pathologically stage I or II disease, and radical resection * Detectable ctDNA in two weeks postoperative plasma sample * No indication for adjuvant chemotherapy according to DCCG guidelines (website) * Age at least 18 years * ECOG performance status 0-2 * Clinically eligible for adjuvant chemotherapy at investigators decision. * Adequate bone marrow, liver and renal function allowing systemic chemotherapy (Absolute neutrophil count ≥1.5x109/l and thrombocytes ≥ 100x109/l. Bilirubin ≤ 1.5 x upper normal value and alanine aminotransferase ≤ 3 x upper normal value, and Calculated or measured renal glomerular filtration rate at least 30 mL/min) * Anticonception for fertile women and for male patients with a fertile partner. Intrauterine device, vasectomy of a female subject's male partner or hormonal contraceptive are acceptable • * Written and verbally informed consent Exclusion Criteria: * Radiological evidence of distant metastasis, by CT- chest and abdomen * Incapacity, frailty, disability and comorbidity to a degree that according to the investigator is not compatible with combination chemotherapy * Previous treatment with 5FU or oxaliplatin * Neuropathy NCI grade \> 1 * Other malignant tumor within 5 years except non-melanoma skin cancer or carcinoma in situ cervicis uteri * Pregnant (positive pregnancy test) or breast feeding women