Exelixis (EXEL) announced detailed results from STELLAR-303, a phase 3 pivotal trial evaluating zanzalintinib in combination with atezolizumab versus regorafenib in patients with previously treated non-microsatellite instability-high metastatic colorectal cancer. As previously announced, the study met one of its dual primary endpoints, demonstrating a 20% reduction in the risk of death with the combination in the intention-to-treat population at the final analysis. At a median follow-up of 18 months, median overall survival in the ITT population was 10.9 months with zanzalintinib in combination with atezolizumab versus 9.4 months with regorafenib. Detailed findings from the study, including OS and progression-free survival in the ITT population and in the subset of patients without liver metastases, are being presented at the 2025 European Society for Medical Oncology Congress during the Proffered Paper Session 2: GI Tumours, Lower Digestive at 9:25 a.m. CEST and simultaneously published in The Lancet. An OS benefit with the combination was consistently observed across pre-specified subgroups, including geographic region, RAS status, liver involvement and prior anti-VEGF therapy, as presented in Table 1 below. The 12- and 24-month landmark OS estimates were 46% and 20%, respectively, for the combination of zanzalintinib and atezolizumab, and 38% and 10%, respectively, for regorafenib. Data pertaining to the other dual primary endpoint, OS in patients without liver metastases, were immature at the data cutoff. A prespecified interim analysis showed a trend in OS favoring the combination at a median follow-up of 16.8 months. The trial will proceed to the planned final analysis for this endpoint. A trend for improvement in PFS with the combination was also observed in the ITT population, though statistical superiority cannot be claimed at this time due to the prespecified hierarchical testing strategy. The trend for PFS improvement with zanzalintinib in combination with atezolizumab versus regorafenib was consistent across subgroups. The safety profiles of zanzalintinib in combination with atezolizumab and of regorafenib were generally consistent with what has been previously observed, and no new safety signals were identified. Grade 3/4 treatment-related adverse events occurred in 59% of patients receiving zanzalintinib in combination with atezolizumab and 37% of patients receiving regorafenib. AEs leading to discontinuation of all study treatment occurred in 18% versus 15% of patients, respectively. The most common grade 3/4 treatment-related AEs were hypertension, fatigue, diarrhea and proteinuria. Deaths considered related to treatment by investigators were two for zanzalintinib, two for atezolizumab, one for the combination and one for regorafenib.
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