On October 20, 2025 Exelixis, Inc. (Nasdaq: EXEL) reported detailed results from STELLAR-303, a global phase 3 pivotal trial evaluating zanzalintinib in combination with atezolizumab (Tecentriq) versus regorafenib in patients with previously treated non-microsatellite instability (MSI)-high metastatic colorectal cancer (CRC). 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 (ITT) population at the final analysis (stratified hazard ratio [HR]: 0.80; 95% confidence interval [CI]: 0.69-0.93; P=0.0045). At a median follow-up of 18.0 months, median overall survival (OS) 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 (PFS) in the ITT population and in the subset of patients without liver metastases, are being presented today at the 2025 European Society for Medical Oncology (ESMO) (Free ESMO Whitepaper) Congress during the Proffered Paper Session 2: GI Tumours, Lower Digestive at 9:25 a.m. CEST and simultaneously published in The Lancet.

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"While treating non-MSI-high metastatic colorectal cancer remains a challenge, the combination of zanzalintinib and atezolizumab has shown consistent benefits across key subgroups of patients," said Anwaar Saeed, M.D., Section Chief of Gastrointestinal Oncology at the University of Pittsburgh, Director of the Gastrointestinal Disease Center at UPMC Hillman Cancer Center and a lead investigator of the trial. "STELLAR-303 is the first immunotherapy-based phase 3 trial that demonstrated improved overall survival with a differentiated kinase inhibitor compared to a standard of care in this patient population. The survival benefit was demonstrated early and was consistent throughout the trial, underscoring the combination’s potential for patients in need of a new and effective treatment option after disease progression."

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% (95% CI: 41-51) and 20% (95% CI: 15-26), respectively, for the combination of zanzalintinib and atezolizumab, and 38% (95% CI: 34-43) and 10% (95% CI: 6-16), respectively, for regorafenib.

TABLE 1

Median OS, months (95% CI)

HR (95% CI)

Zanzalintinib + Atezolizumab

Regorafenib

Geographic region

Asia

11.5 (9.2-13.7)

8.8 (7.8-10.4)

0.77 (0.59-1.00)

Rest of the world

10.9 (9.3-12.3)

9.8 (8.3-10.9)

0.82 (0.68-0.99)

RAS status

Wild type

12.0 (10.1-14.6)

10.4 (8.7-12.3)

0.79 (0.61-1.01)

Mutant

10.3 (9.0-11.9)

8.7 (8.1-9.8)

0.80 (0.66-0.98)

Active liver metastases

Presence

8.9 (8.0-9.9)

7.7 (6.5-8.5)

0.78 (0.65-0.94)

Absence

15.9 (13.5-17.6)

12.8 (10.9-15.5)

0.77 (0.59-1.01)

Prior anti-VEGF antibody treatment

Yes

10.6 (9.3-12.5)

8.8 (8.3-9.9)

0.80 (0.68-0.95)

No

11.5 (8.7-13.5)

11.1 (9.5-12.6)

0.80 (0.56-1.15)

OS = overall survival; CI = confidence interval; HR = hazard ratio; VEGF = vascular endothelial growth factor

Data pertaining to the other dual primary endpoint, OS in patients without liver metastases (non-liver metastases, NLM), were immature at the data cutoff. A prespecified interim analysis showed a trend in OS favoring the combination (15.9 months versus 12.8 months; stratified HR: 0.79; 95% CI: 0.61-1.03; P=0.0875) at a median follow-up of 16.8 months. The trial will proceed to the planned final analysis for this endpoint.

"These detailed results from STELLAR-303 provide further insight into the combination of zanzalintinib and atezolizumab as a potential new option to extend survival in patients with previously treated metastatic colorectal cancer," said Dana T. Aftab, Ph.D., Executive Vice President, Research and Development, Exelixis. "Before the end of this year, we intend to complete the submission of our first new drug application for zanzalintinib as we work toward bringing this combination regimen to a patient community seeking a new and chemotherapy-free option. These data, along with our robust clinical trial program, underscore the progress we are making toward our goal of increasing the scope and scale of the solid tumor types zanzalintinib may help address."

A trend for improvement in PFS with the combination was also observed in the ITT population (stratified HR: 0.68 [95% CI: 0.59–0.79]; median, 3.7 [95% CI: 3.5–3.8] months versus 2.0 [95% CI: 1.9–2.6] months), 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 (AEs) 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 (15% versus 9%, respectively), fatigue (6% versus 2%), diarrhea (6% versus 2%) and proteinuria (6% versus 2%). Deaths considered related to treatment by investigators were two for zanzalintinib, two for atezolizumab, one for the combination and one for regorafenib.

About STELLAR-303
STELLAR-303 (NCT05425940) is a global, multicenter, randomized, phase 3, open-label study that randomized patients 1:1 to either zanzalintinib in combination with atezolizumab (n=451) or regorafenib (n=450). The study includes patients with previously treated non-MSI-high metastatic CRC. The dual primary endpoints of the study are OS in the ITT population and in the NLM subgroup of patients. The ITT population consisted of all randomized patients, regardless of the presence of liver metastases. The NLM subgroup consisted of patients who did not have active liver metastases at baseline as determined by investigator assessment. Secondary endpoints include PFS, objective response rate and duration of response in the ITT population and in the NLM subgroup of patients. More information about the trial is available at ClinicalTrials.gov.

About Zanzalintinib
Zanzalintinib is a novel oral kinase inhibitor that inhibits the activity of the TAM kinases (TYRO3, AXL, MER), MET and VEGF receptors. These kinases play important roles in oncogenic processes including tumor cell proliferation, metastasis, angiogenesis, drug resistance and evasion of antitumor immunity. With zanzalintinib, Exelixis sought to build upon its extensive experience with the target profile of cabozantinib, the company’s flagship medicine, while improving key characteristics, including pharmacokinetic half-life. Zanzalintinib is currently being developed for the treatment of advanced solid tumors, including colorectal cancer, kidney cancer and neuroendocrine tumors.

Zanzalintinib is an investigational agent that is not approved for any use and is the subject of ongoing clinical trials.

About CRC
CRC is the third most common cancer and the second leading cause of cancer-related deaths in the U.S.1 Approximately 154,000 new cases will be diagnosed in the U.S. with around 53,000 expected deaths from the disease in 2025.1 CRC is most frequently diagnosed among people aged 65-74 and is more common in men and in people of non-Hispanic American Indian/Alaska Native descent.2 Nearly a quarter of CRC cases are diagnosed at the metastatic stage, at which point the five-year survival rate is just 16.2%.2 The liver is the most common site for CRC metastasis. Liver metastases significantly impact survival, with a median five-year survival rate of less than 14% when treated with palliative chemotherapy.

(Press release, Exelixis, OCT 20, 2025, View Source [SID1234656814])