The LUNAR1 Test (Guardant Health, Redwood City, CA, USA) will be used for ctDNA determination. For the efficacy analysis, the PEGASUS cohort will be compared with a cohort of 420 patients from the TOSCA trial (NCT00646607) population matched 3:1 for all known prognostic phenotypes.

A post-surgical LB executed 2-4 weeks after surgery will guide a "Molecular Adjuvant" treatment as follows: i) ctDNA+ patients will receive CAPOX for 3 months; ii) ctDNA- patients will receive capecitabine (CAPE) for 6 months but will be retested after 1 cycle, and if found ctDNA+ will be switched to CAPOX treatment.

Immediately after the end of the "Molecular Adjuvant" treatment a further LB will be performed and instruct subsequent treatment. Positive patients (ctDNA+/+ and ctDNA-/+) will receive an up-scaled "Molecular Metastatic" systemic treatment for 6 months or until radiological progression or toxicity as follows: i) ctDNA+/+ patients will be treated with FOLFIRI; ii) ctDNA-/+ patients with CAPOX. These patients will be subjected to a LB after 3 months at the end of treatment and in case of positivity will be switched to FOLFIRI.

Patients experiencing ctDNA conversion to negative (ctDNA+/-) will receive a de-escalated treatment with CAPE for 3 months. 3 LB will be performed within 3 months and in case of positivity the patient will be switched to FOLFIRI. Patients with ctDNA-/- will be subjected to an interventional follow-up comprising 2 further LB and in case of positivity they will be switched to CAPOX treatment. PEGASUS is piggybacked to AlfaOmega (NCT04120935), a Master Observational Protocol that will follow patients from diagnosis to 5 years or recurrence/death (whichever comes first), collecting clinical data, radio-images and biological samples. AlfaOmega provides a clinical and logistic ecosystem for the seamless integration of PEGASUS clinical results with the biological underpinning of colon cancer.