Here’s a stark reality: Microsatellite-stable (MSS) metastatic colorectal cancer remains one of the most stubborn challenges in oncology, especially after patients have exhausted standard treatments like chemotherapy and targeted therapies. Shockingly, nearly 95% of colorectal cancers fall into this category, and they’re notoriously resistant to immunotherapy. This leaves doctors with limited options like regorafenib or trifluridine/tipiracil, which offer modest benefits at best and come with significant side effects (Grothey et al., Lancet, 2013). But here’s where it gets exciting: Zanzalintinib, a next-generation multi-kinase inhibitor developed by Exelixis, is emerging as a game-changer in tackling the angiogenic and microenvironment-driven resistance that makes MSS colorectal cancer so difficult to treat.
Why is this such a big deal? Because MSS colorectal cancer is aggressive, immunologically 'cold' (meaning it doesn’t respond well to immune-boosting therapies), and resistant to checkpoint inhibitors. It’s characterized by low mutation rates, high blood vessel growth (angiogenesis), a hostile environment that keeps immune cells out, and a strong tendency to spread (metastasize). Zanzalintinib takes aim at these very features by targeting key pathways like VEGFR2, MET, AXL, and the TAM kinase family. These pathways are responsible for tumor growth, spread, and immune evasion. By blocking them simultaneously, zanzalintinib not only stifles blood vessel formation but also reverses immune evasion, making the tumor more vulnerable to attack.
And this is the part most people miss: Early studies suggest zanzalintinib’s shorter half-life and improved kinase selectivity may lead to better tolerability and more predictable outcomes compared to its predecessor, cabozantinib (Gao et al., Clin Cancer Res, 2021). This means patients could potentially stay on treatment longer, which is crucial for managing advanced cancer.
The STELLAR-303 trial put zanzalintinib to the test in patients with MSS metastatic colorectal cancer who had already failed multiple treatments, including chemotherapy and bevacizumab. These patients were randomized to receive either zanzalintinib or regorafenib, the current standard of care. The results? Zanzalintinib outperformed regorafenib in both overall survival and progression-free survival, marking the first significant breakthrough in MSS colorectal cancer in nearly a decade. Even patients with liver metastases, who typically respond poorly to immunotherapy, saw consistent benefits (STELLAR-303 Investigators, ASCO GI, 2025).
While the exact survival numbers are still pending, the trial showed that zanzalintinib led to more durable responses and fewer treatment discontinuations. Its side effect profile, though typical for anti-angiogenic drugs (think hypertension, fatigue, and hand-foot syndrome), was more manageable than regorafenib’s, thanks to its optimized design. This could mean better adherence and longer treatment durations—a win for patients in later stages of the disease.
But here’s the controversial part: Could zanzalintinib replace regorafenib as the new standard of care for MSS colorectal cancer? And how will it fit into combination therapies, especially with immunotherapy, where preclinical data suggest it could enhance immune responses (Feng et al., Cancer Res, 2022)? These questions are already sparking debates in the oncology community.
Looking ahead, zanzalintinib is being explored in other cancers driven by MET or AXL signaling, such as renal cell carcinoma and hepatocellular carcinoma. As more data emerge, it could become a cornerstone of modern targeted therapy, addressing the biological complexity of advanced cancers.
So, what do you think? Is zanzalintinib the breakthrough MSS colorectal cancer patients have been waiting for? Or is it just another step in a long journey? Let us know in the comments below!
For more insights, check out our detailed coverage on Colorectal Cancer and the STELLAR-303 Trial on OncoDaily. And don’t forget to subscribe to our YouTube channel for the latest updates in oncology.
Written by Armen Gevorgyan, MD
