This is a multi-site epidemiological study designed to monitor circulating tumor DNA (ctDNA) status in participants with Stage II (high risk)/III colorectal cancer (CRC) following resection/prior to adjuvant chemotherapy (AdCTx), during the course of AdCTx and for a period of up to 630 days (21 months) thereafter, according to CRC stages and disease characteristics. Participants receive no therapeutic intervention as part of this study. This study will identify participants with confirmed Stage II (high risk)/III CRC that are positive for ctDNA after resection who might be potential candidates for the clinical study BNT122-01 (NCT04486378), a study of RO7198457 after completion of standard adjuvant chemotherapy in this patient population. These participants will have the option to enter screening for BNT122-01 at Screening Visit 2 of that study if they meet the eligibility criteria of BNT000-001 during screening. Data from the assessments from this study (BNT000-001) will be carried across to the BNT122-01 study where feasible.