PD-1 Inhibitor Effective in MSI-High Locally Advanced Rectal Cancer

In rectal cancer, the standard approach of preoperative chemoradiotherapy followed by surgery and adjuvant chemotherapy is being replaced by total neoadjuvant therapy, with patients who achieve a clinical complete response potentially avoiding surgery. Microsatellite instability (MSI)-high rectal cancers represent a rare subset of rectal cancers that may be highly responsive to immune checkpoint inhibitors.

Investigators now report results of a single institution, investigator-initiated phase 2 trial evaluating the anti–PD-1 agent dostarlimab as primary treatment for locally advanced rectal cancer. Patients with DNA mismatch repair protein–deficient rectal cancer detected by immunohistochemistry received intravenous dostarlimab (500 mg) ever…