Zanzalintinib: How Exelixis Built a Smarter Cabozantinib Successor for Kidney Cancer |

From Cabozantinib to Zanzalintinib: What Drove the Redesign?

Cabozantinib has been a cornerstone of advanced renal cell carcinoma treatment since its FDA approval in 2016, earning indications as both monotherapy and in combination with nivolumab. However, real-world prescribing data reveal that a substantial proportion of patients require dose reductions — some studies reporting rates exceeding 50% — primarily due to diarrhea, palmar-plantar erythrodysesthesia, and fatigue. These tolerability challenges limit the drug's full therapeutic potential and can compromise treatment duration.

Exelixis undertook a medicinal chemistry campaign guided by X-ray crystallographic data of cabozantinib bound to its kinase targets. The goal was to identify structural modifications that would maintain potent inhibition of VEGFR1-3, MET, and TAM family kinases (AXL and MER) — the targets most strongly associated with anti-tumor activity in RCC — while reducing engagement with kinases implicated in off-target toxicities. Preclinical pharmacology studies published by Exelixis scientists indicated that the resulting molecule, zanzalintinib, achieved improved potency ratios against priority targets relative to those linked to thyroid hormone metabolism disruption. This rational design approach represents a broader trend in oncology drug development: rather than discovering entirely new targets, refining existing validated mechanisms for better therapeutic windows.

What Phase 3 Trials Are Testing Zanzalintinib in Kidney Cancer?

Non-clear cell renal cell carcinoma accounts for roughly 20–25% of all kidney cancers and encompasses diverse histological subtypes including papillary, chromophobe, and collecting duct variants. Unlike clear cell RCC, where multiple immunotherapy-TKI combinations have demonstrated survival benefits, non-clear cell patients are typically excluded from pivotal trials, leaving clinicians to extrapolate from limited subgroup analyses. The STELLAR-304 trial (NCT05525520) specifically targets this underserved population, randomizing patients to zanzalintinib 100 mg daily plus nivolumab versus sunitinib 50 mg on a 4-weeks-on/2-weeks-off schedule.

The trial's co-primary endpoints are progression-free survival and overall survival, with secondary endpoints including objective response rate, duration of response, and patient-reported quality of life measures. Enrollment is being conducted across sites in North America, Europe, and Asia-Pacific. Beyond STELLAR-304, Exelixis has indicated plans for additional RCC-focused development, including potential combinations with other checkpoint inhibitors. The company's broader STELLAR clinical program encompasses trials across colorectal cancer, non-small cell lung cancer, and other tumor types, providing a growing safety database that will inform kidney cancer-specific risk-benefit assessments. Investigators anticipate that positive Phase 3 results could support an FDA supplemental application specifically for renal cell carcinoma indications.