Randomized Trial of Standard Chemotherapy Alone or Combined With Atezolizumab as Adjuvant Therapy for Patients With Stage III Colon Cancer and Deficient DNA Mismatch Repair


Primary Objective:

  • To determine whether atezolizumab combined with oxaliplatin, leucovorin calcium, and fluorouracil (FOLFOX) and its continuation as monotherapy can significantly improve disease-free survival (DFS) compared to FOLFOX alone in patients with stage III colon cancers and deficient DNA mismatch repair (dMMR).

Secondary Objectives:

  • To determine whether atezolizumab combined with FOLFOX and its continuation as monotherapy can significantly improve overall survival compared to FOLFOX alone in patients with stage III colon cancers and dMMR.
  • To assess the adverse events (AE) profile and safety of each treatment arm, using the Common Terminology Criteria for Adverse Events (CTCAE) and patient-related outcomes (PRO)-CTCAE.

Study Arms

  • Experimental: Arm I (combination chemotherapy, atezolizumab)
  • Active Comparator: Arm II (combination chemotherapy)


  • Histologically proven stage III colon adenocarcinoma (any T [Tx, T1, T2, T3, or T4], N1-2M0; includes N1C); tumors must be deemed to originate in the colon including tumors that extend into/involve the small bowel (e.g. those at the ileocecal valve)
  • Presence of deficient (d) DNA mismatch repair (dMMR); MMR status must be assessed by immunohistochemistry (IHC) for MMR protein expression (MLH1, MSH2, MSH6, PMS2) where loss of one or more proteins indicates dMMR; dMMR may be determined either locally or by site-selected reference lab; Note: loss of MLH1 and PMS2 commonly occur together; formalin-fixed paraffin-embedded (FFPE) tumor tissue is required for subsequent retrospective central confirmation of dMMR status
  • Patients with testing that did not show dMMR (loss of MMR protein) are not eligible to participate; patients whose tumors show MSI-H by polymerase chain reaction (PCR)-based assay are not eligible to participate unless they also have MMR testing by IHC and are found to have dMMR (i.e. loss of one or more MMR proteins)
  • Patients who are known to have Lynch syndrome and have been found to carry a specific germline mutation in an MMR gene (MLH1, MSH2, MSH6, PMS2) are eligible to participate
  • Tumors must have been completely resected; in patients with tumor adherent to adjacent structures, en bloc R0 resection must be documented in the operative report or otherwise confirmed by the surgeon; near or positive radial margins are acceptable so long as en bloc resection was performed. Proximal or distal margin positivity is not permitted
  • Entire tumor must be in the colon (rectal involvement is an exclusion); surgeon confirmation that entire tumor was located in the colon is required only in cases where it is important to establish if the tumor is a colon versus (vs.) rectal primary
  • Based upon the operative report and other source documentation, the location of the primary tumor will be categorized as proximal or distal to the splenic flexure (distal includes), and further categorization will be as follows: cecum/ascending, descending, sigmoid colon, or rectosigmoid colon
  • No evidence of residual involved lymph node disease or metastatic disease at the time of registration based on clinician assessment of imaging; the treating physician will determine if incidental lesions on imaging require workup to exclude metastatic disease; if based on review of images, the treating physician determines the patient to be stage III, then the patient is eligible
  • No prior medical therapy (chemotherapy, immunotherapy, biologic or targeted therapy) or radiation therapy for the current colon cancer except for one cycle of mFOLFOX6
  • Eastern Cooperative Oncology Group (ECOG) performance status =< 2