Combination Immunotherapy in Colorectal Cancer

Resected tumors will be examined in their entirety, and regression of resected tumors was assessed by estimating the percentage of residual viable tumor of the macroscopically identifiable tumor bed, as identified on routine hematoxylin and eosin (H&E) staining. In addition, regression will be classified using the Mandard tumor regression grading system. Major pathologic response (MPR) will be defined as ≤10% of residual viable tumor cells (or ≥ 90% response), corresponding to Mandard tumor regression grade 1 (CR) or 2 (near-CR). PR will be defined as at least 50% tumor regression. However, considering the lack of consensus on the definition of PR after immunotherapy, tumors with >50% and <90% residual viable tumor will be labeled accordingly as '10-50% tumor regression', as per the NICHE study (Chalabi et. al., 2020). When analyzing pMMR responders versus pMMR nonresponders, this subgroup will be included in the group of nonresponders.

Safety will be assessed by evaluation of the number of participants experiencing SAEs according to the Common Terminology Criteria for Adverse Events (CTCAE) v5.0 at 90 days post-the last dose of study drug. Grade 3 or 4 adverse event possibly, probably or definitely attributed to bot/bal. Patients from cohorts B and C were not included in the analysis of this outcome measure per study protocol.

Any AEs or SAEs that lead to a delay in surgery greater than 12 weeks from treatment initiation (Day 0) will be recorded. If there are ≥ 2 patients out of the first 6 patients, or ≥ 4 patients out of the full 12 participants (≥33%), with AEs/SAEs that lead to a delay in surgery beyond 12 weeks from treatment initiation, with the exception of COVID-related procedural delays, then this combination of botensilimab and balstilimab, at these dosages will not be considered feasible in this population.

The joint patient-surgeon decision to defer surgery for a watch and wait (Watch-&-Wait W&W) approach is allowed as long as the patient is demonstrating sustained response as determined by clinical, radiographic, endoscopic, and/or blood-based biomarkers. For participants who elect to undergo surgery, pathological response will be determined as described above. The key endpoint here will be "Major pathological response (MPR; CR + near-CR). Patients who opt for non-operative management based on clinical response will be considered to have CR. Complete response will be determined by the treating physician and surgeon based on composite subjective and objective assessments of clinical, radiographic, endoscopic, blood-based biomarker assessments, and/or the absence of clinical and radiographic progression.

Summary statistics including mean, standard deviation will be provided for ctDNA levels obtained at various time points. Linear mixed-effects models will be used to model longitudinal biomarker values. Simultaneous testing of general linear hypotheses will be used to evaluate contrasts of interest.

Median and range will be provided for ctDNA levels obtained at various time points. Linear mixed-effects models will be used to model longitudinal biomarker values. Simultaneous testing of general linear hypotheses will be used to evaluate contrasts of interest.