Retrospective data suggests patients with MSI-high rectal cancer might not just respond poorly to standard neoadjuvant chemoradiation (TNT), but their disease could actually progress. This makes immunotherapy a potentially safer and more effective first-line neoadjuvant choice, not just an alternative.
Even with negative biopsies, post-immunotherapy scans and scopes can show residual masses or mucin pools that are mistaken for active cancer. This makes determining a true complete clinical response difficult and can lead to unnecessary surgeries where no cancer is found, as these changes can take years to resolve.
Unlike rectal cancer where MRI is effective, there is no reliable imaging to monitor for complete response in colon cancer. The alternative, frequent colonoscopies, is impractical and unsafe. This lack of viable surveillance tools makes non-operative management too risky, even with promising response rates to immunotherapy.
Patients showing a near-complete response at the end of a six-month immunotherapy course may still convert to a full complete response two months later without additional treatment. Clinicians should consider 'holding their nerve' and re-evaluating with repeat imaging before altering the treatment plan.