Long-term follow-up of a phase 2 trial of neoadjuvant pembrolizumab for locally advanced dMMR/MSI-H solid tumors

Neoadjuvant immunotherapy can induce pathologic complete response (pCR) in patients with localized dMMR/MSI-H tumors. Long-term outcomes of these patients are unknown, as is the clinical utility of measuring circulating tumor DNA (ctDNA). Long-term follow-up of a phase 2 trial at MD Anderson Cancer Center (Houston, TX) found that three-year EFS and OS rates after neoadjuvant pembrolizumab for locally advanced dMMR/MSI-H solid tumors were 80% (95% CI 66-93) and 94% (86-100), respectively. Patients without detectable ctDNA after pembrolizumab had higher 3-year EFS and OS rates than patients with detectable ctDNA after pembrolizumab (both p<0.001). Patients with CRC who were managed non-operatively and had undetectable ctDNA after pembrolizumab had a higher 2-year EFS rate than patients with detectable ctDNA after pembrolizumab (100% versus 33%; p=0.03). The authors conclude that neoadjuvant pembrolizumab demonstrated long-term efficacy in patients with locally advanced dMMR/MSI-H tumors.