• Patients must be a man or woman of at least 18 years of age.

• Patients must have Stage II/Stage III rectal cancer or Stage II (high risk)/Stage III colon cancer per American Joint Committee on Cancer (AJCC) 2017 that has been surgically totally resected (R0 confirmed by pathology report). Stage II (high risk) colon cancer is defined as Stage II disease with any of the following risk factors for recurrence:

‣ T4

⁃ Grade ≥ 3.

⁃ Clinical presentation with bowel obstruction or perforation.

⁃ Histological signs of vascular, lymphatic or perineural invasion.

⁃ \< 12 nodes evaluated after surgery.

• For the CLM Cohort: patients must have metastatic colorectal cancer (mCRC) (Stage IV) with resected CLM (synchronous and metachronous CLM within 6 months of initial diagnosis) per AJCC 2017, after standard of care (SoC) primary resection and curative-intent hepatectomy (R0 confirmed by pathology report) with or without (neo-)adjuvant chemotherapy (prior to hepatectomy), and planned adjuvant chemotherapy.

∙ For the Biomarker Cohort: patients with tumors of the colon, including but not limited to, colon adenocarcinoma, carcinoid tumors (including goblet cell carcinoid/adenocarcinoma), and tumors of the appendix, whose tumors were surgically resected and are planned for adjuvant chemotherapy (per institutional standards), can be included.

• Patients must have detectable ctDNA prior to start of adjuvant chemotherapy (AdCTx) (except for the Biomarker Cohort).

‣ ctDNA assay must be performed through this trial or study BNT000-001 ctDNA screening protocol.

• Patients must have an Eastern Cooperative Oncology Group Performance Status of 0-1.

• Patients must have adequate hematologic, bone marrow and organ function as defined by the protocol.

• Adequate tumor material in formalin-fixed paraffin embedded blocks or as sectioned tissue (only upon approval by sponsor) must be available (as described in the laboratory manual). For the CLM Cohort: tumor material must come from primary resection for patients who undergo staged approach, or from available archival material from the previously untreated tumor biopsy from the primary.

• At least 5 tumor neoantigens identified in the provided tumor sample.

• The patient has started a standard of care AdCTx preferably within 8 weeks but no later than 10 weeks post-surgery and has completed at least 3 months of treatment of a 3- or a 6-month course of chemotherapy (including rest days). For the CLM Cohort: patient must have completed AdCTx with or without (neo-)adjuvant chemotherapy for up to 6 months in total or total intended amount determined by care providers per SoC. AdCTx must have started preferably within 8 weeks, but no later than 10 weeks, after hepatectomy. For the Biomarker Cohort: patient must have received at least one cycle of adjuvant chemotherapy per institutional standards.