Epidemiological Study to Monitor Study Participants With Resected Stage II (High Risk) or Stage III Colorectal Cancer for Circulating Tumor DNA Before, During and After Their Treatment With Adjuvant Chemotherapy

Inclusion Criteria: * Must have given informed consent indicating that they understand the purpose of and procedures required for the study and are willing to participate in the study. * Age ≥ 18 years old at time of signing the informed consent form. * Ability to comply with the study protocol, in the investigator's judgment. * Must have Stage II/Stage III rectal cancer or Stage II (high risk)/Stage III colon cancer per AJCC 2017 that has been surgically totally resected (R0 confirmed by pathology report). Stage II (high risk) colon cancer is defined as (any of): * T4 * Grade ≥ 3 * Clinical presentation with bowel obstruction or perforation * Histological signs of vascular, lymphatic or perineural invasion * \< 12 nodes examined * Adequate tumor material in formalin-fixed paraffin embedded blocks or as sectioned tissue (only upon approval by sponsor) must be available, preferably from resection. The specimen should be submitted along with an associated pathology report. Multiple samples may be provided as available, but priority should be given to tissue with the highest tumor content and lowest necrotic area. * Intention to receive a standard of care AdCTx within 8 weeks post-surgery, and be scheduled for at least 3 months of treatment (including rest days) according to the treating physician or investigator. * Eastern Cooperative Oncology Group Performance Status of 0 or 1. * Adequate end-organ function. Exclusion Criteria: * Neo-adjuvant (radio)chemotherapy prior to surgery. * Prior systemic investigational therapy. * Active Hepatitis B virus (HBV) infection. * Active hepatitis C virus (HCV) infection. * History of human immunodeficiency virus (HIV) antibody positivity. * Residual tumor classification following surgery other than R0 (microscopic margin-negative resection). * Participants with known past or current malignancy other than inclusion diagnosis, except for: * Cervical carcinoma of Stage 1B or less. * Non-invasive basal cell or squamous cell skin carcinoma. * Non-invasive, superficial bladder cancer. * Prostate cancer with a current prostate-specific antigen level \< 0.1 ng/mL. * Any curable cancer with a complete response of \> 2 years duration. * Participant has not started standard of care AdCTx within 8 weeks post-surgery. * Participant has received less than 3 months (including rest days) of AdCTx treatment. * Inadequate tumor material (either quality or quantity) to support ctDNA analysis. * Participants who have had prior splenectomy. * Participants with diagnosed microsatellite instability high tumors.