A Phase Two, Single-Arm, Open-Label Study With Dostarlimab Monotherapy in Participants With Untreated Stage II/III dMMR/MSI-H Locally Advanced Rectal Cancer (AZUR-1).

Background: Colorectal cancer (CRC) had the second highest cancer mortality worldwide in 2020; nearly a third of CRCs were rectal cancers (RC). A recent study demonstrated that dostarlimab, an immune-checkpoint inhibitor, was highly effective in treating mismatch repair deficient (dMMR) locally advanced RC as all included patients had a clinical complete response (cCR) without radiation or chemotherapy. This study's objective is to evaluate the efficacy and safety of dostarlimab monotherapy in patients with previously untreated locally advanced dMMR RC.

Patients/methods: AZUR-1 (NCT05723562) is a multicenter, open-label, nonrandomized, single-arm phase 2 study enrolling approximately 150 patients across 10 countries. Key eligibility criteria include dMMR status or microsatellite instability-high (MSI-H) phenotype. Dostarlimab 500 mg will be administered intravenously every 3 weeks for 9 cycles. The primary endpoint is cCR by independent central review (ICR) at 12 months. Key secondary endpoints include cCR by ICR at 24 and 36 months, and 3-year event-free survival by investigator assessment. Additional secondary endpoints include organ preservation rate at 3 years and disease-specific survival and overall survival at 5 years. Efficacy and safety will be assessed in all patients who receive ≥1 dose of dostarlimab. All patients will be followed for 5 years (unless consent is withdrawn).

Conclusions: AZUR-1 will evaluate the efficacy of dostarlimab immunotherapy in dMMR/MSI-H RC. Utilizing novel aspects including long follow-up of all patients and standardization of clinical response assessment, this study will provide international multicentric data to evaluate tumor response in an immunotherapy setting and new evidence on long-term outcomes.