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.

Individual participants will be involved in the study for at least 12 months to up to 29 months (maximum follow-up 21 months after completion of AdCTx [Visit 10]). For all participants who transfer to BNT122-01 (NCT04486378), study participation in BNT000-001 will end at time of screening for BNT122-01.

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.

Participants with Stage II (high risk)/III CRC after resection (R0) and that are scheduled to receive AdCTx will be enrolled in this study.