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Background: Our study aimed to evaluate the efficacy and feasibility of neoadjuvant anti–PD-1 treatment for localized mismatch repair–deficient (dMMR) colorectal cancer (CRC). Patients and Methods: The study cohort included patients with localized dMMR CRC who received PD-1 inhibitors as neoadjuvant therapy from 3 medical centers in Southern China. Main eligibility criteria included age between 18 and 75 years, ECOG performance status of 0 or 1, and receipt of ≥2 doses of PD-1 inhibitors. Results: A total of 73 patients were included. Most of the tumors were locally advanced, including 19 (26.0%) T4a and 29 (39.7%) T4b. Most patients (79.5%) received PD-1 inhibitor monotherapy. Objective response per radiologic assessment was achieved in 62 (84.9%) patients, including 17 (23.3%) with complete response (CR) and 45 (61.6%) with partial response, with a median time to response of 9.6 weeks. Patients with T4a/4b disease had a similar response rate as those with T2–3 disease (84.0% vs 85.4%; P=.999). As of writing, a total of 50 patients have undergone surgery. Pathologic CR was achieved in most (57.1%) patients and remained high (59.5%) even among the 38 patients with T4a/4b disease. The 17 patients with CR did not undergo surgery and adopted a watch-and-wait strategy. After a median follow-up of 17.2 months (range, 3.4–45.1 months), the overall median recurrence-free and overall survivals were not reached. Among patients undergoing surgery or achieving CR, the 2-year tumor-specific disease-free and overall survival rates were both 100%. During neoadjuvant treatment, grade 3–4 adverse events occurred in 8 patients; 4 required acute intervention. Severe postoperative complications were recorded in 4 patients, 3 of whom required a second surgery. Conclusions: Neoadjuvant therapy with PD-1 blockade is highly effective for localized dMMR CRC, with an acceptable safety profile and low recurrence rate. This treatment holds promise for becoming the new standard of care for localized dMMR CRCs.

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.