Complete Pathological Response After Neoadjuvant Short-Course Immunotherapy with Ipilimumab and Nivolumab in Locally Advanced MSI-H/dMMR Rectal Cancer.

Immune checkpoint inhibitors are more active in treatment-naïve patients than in patients with refractory high-grade microsatellite instability (MSI-H)/deficiency in mismatch repair (dMMR) colorectal cancer. Standard neoadjuvant chemoradiation is less effective in MSI-H/dMMR rectal cancer patients than in patients with proficient mismatch repair. A young patient with Lynch syndrome and MSI-H/dMMR locally advanced rectal cancer refused chemoradiation in order to preserve his fertility. After neoadjuvant treatment with one dose of ipilimumab and two doses of nivolumab a complete clinical and pathological response was documented. Clinical trials are needed to first establish neoadjuvant treatment with immune checkpoint inhibitors in patients with locally advanced MSI-H/dMMR rectal cancer and thereafter to evaluate organ-preservation strategies.