Long-Term Outcomes of dMMR/MSI-H Rectal Cancer Treated With Anti–PD-1–Based Immunotherapy as Curative-Intent Treatment

Abstract

Background: Neoadjuvant anti–PD-1 therapy has shown encouraging efficacy in patients with deficient DNA mismatch repair (dMMR)/microsatellite instability-high (MSI-H) locally advanced rectal cancer (LARC), which suggests its potential as a curative-intent therapy and a promising treatment option for organ preservation. We aimed to investigate the long-term outcomes of patients with dMMR/MSI-H LARC who experienced clinical complete response (cCR) after anti–PD-1 therapy. Methods: We retrospectively analyzed patients with dMMR/MSI-H LARC who achieved cCR and received nonoperative management following neoadjuvant anti–PD-1–based treatment from 4 Chinese medical centers. Patients were followed up for at least 1 year after they achieved cCR, their clinical data were collected, and survival outcomes were analyzed using the Kaplan-Meier method. Results: A total of 24 patients who achieved cCR and received nonoperative management from March 2018 to May 2022 were included, with a median age of 51.0 years (range, 19.0–77.0 years). The median treatment course to reach cCR was 6.0 (range, 1.0–12.0). Fifteen patients (62.5%) continued their treatments after experiencing cCR, and the median treatment course was 17.0 (range, 3.0–36.0). No local regrowth or distant metastasis was observed in a median follow-up time of 29.1 months (range, 12.6–48.5 months) after cCR. The 3-year disease-free and overall survivals were both 100%. Conclusions: Patients with dMMR/MSI-H locally advanced or low-lying rectal cancer who achieved cCR following anti–PD-1–based therapy had promising long-term outcomes. A prospective clinical trial with a larger sample size is required to further validate these findings.