Deficient mismatch repair (dMMR)/microsatellite instability-high (MSIH) colorectal cancer is resistant to conventional chemotherapy but responds to immune checkpoint inhibition (ICI). We review the standard of care in locally advanced dMMR rectal cancer with a focus on ICI. We also present a case report to highlight the treatment complexities and unique challenges of this novel treatment approach. ICI can lead to immune related adverse events (irAEs), resulting in early treatment discontinuation as well as new challenges to surveillance and surgical management. Overall, neoadjuvant ICI can lead to robust treatment responses, but its impact on durable response and organ preservation requires further study.
Keywords: CTLA-4; PD-1; colorectal; dMMR; immunotherapy.