Clinical Scorecard: Systematic Review and Meta-Analysis of Immunotherapy for Non-Surgical Treatment of Colorectal Cancer with Deficient Mismatch Repair (dMMR) and High Microsatellite Instability (MSI-H)

At a Glance

Key Highlights

• Non-operative management ('watch-and-wait') after immunotherapy yields excellent oncologic outcomes with 2-year recurrence-free survival near 100% and local relapse below 2%.
• Organ preservation rates exceed 90%, significantly higher than conventional chemoradiotherapy approaches for rectal cancer.
• Immune-related adverse events are generally low grade; severe toxicities are infrequent and manageable, with rare treatment-related mortality.

Guideline-Based Recommendations

Diagnosis

• Confirm dMMR/MSI-H status via histopathology and molecular testing before immunotherapy initiation.
• Assess complete clinical response (cCR) using standardized criteria post-immunotherapy.

Management

• Consider immune checkpoint inhibitors as first-line treatment for metastatic dMMR/MSI-H colorectal cancer.
• In locally advanced dMMR/MSI-H colorectal cancer achieving cCR, a non-operative 'watch-and-wait' strategy may be employed to preserve organ function.
• Select patients carefully for non-operative management, considering tumor site, response, and patient factors.

Monitoring & Follow-up

• Implement rigorous surveillance protocols to detect local regrowth or distant metastases during follow-up.
• Monitor for immune-related adverse events and manage promptly according to severity.
• Plan for salvage surgery in rare cases of local regrowth.

Risks

• Potential for late recurrence due to limited long-term follow-up data.
• Heterogeneity in treatment regimens and response assessment may affect outcomes.
• Risk of immune-related toxicities including rare severe events and treatment-related mortality.

Patient & Prescribing Data

Patients with locally advanced or metastatic dMMR/MSI-H colorectal cancer, including rectal and select colon cancers, often elderly or frail.

Immunotherapy regimens vary from single-agent PD-1 inhibitors to combination checkpoint blockade; all show high response rates but differing toxicity profiles, underscoring the need for standardized protocols.

Clinical Best Practices

• Use standardized criteria for assessing complete clinical response post-immunotherapy before omitting surgery.
• Adopt a multidisciplinary approach involving oncology, surgery, and radiology for patient selection and monitoring.
• Educate patients on the benefits and risks of non-operative management and the importance of adherence to follow-up.
• Prepare for salvage surgery in the event of local regrowth to maintain oncologic safety.
• Report outcomes stratified by tumor site and treatment regimen to inform future protocols.

References

• KEYNOTE and CheckMate trials on immunotherapy in metastatic dMMR CRC
• Cercek et al. study on neoadjuvant immunotherapy in locally advanced rectal cancer
• Memorial Sloan Kettering Cancer Center series on non-operative management
• MD Anderson cohort on disease control and re-challenge after immunotherapy
• Conventional chemoradiotherapy outcomes in rectal cancer