Belzutifan+Lenvatinib Beats Cabozantinib in Phase 3, But OS Gap and Dual-Drug Cost Threaten Global Access

FDA Approves WELIREG Plus LENVIMA for Advanced ccRCC

Merck and Eisai announced that the U.S. FDA has approved WELIREG (belzutifan) plus LENVIMA (lenvatinib) for adult patients with advanced clear cell renal cell carcinoma (ccRCC) who have previously been treated with a PD-1/PD-L1 inhibitor. This approval is based on the Phase 3 LITESPARK-011 trial, which showed a statistically significant and clinically meaningful improvement in progression-free survival (PFS) for the combination compared to cabozantinib. The combination reduced the risk of disease progression or death by 26% (HR=0.74) and achieved a median PFS of 14.6 months versus 10.6 months for cabozantinib. The objective response rate (ORR) was also significantly improved at 53% compared to 40%.

• The Phase 3 LITESPARK-011 trial demonstrated superior efficacy for WELIREG plus LENVIMA, achieving a median progression-free survival (PFS) of 14.6 months compared to 10.6 months for cabozantinib, representing a 26% reduction in the risk of disease progression or death (HR=0.74; p=0.001). The objective response rate (ORR) was also significantly higher at 53% versus 40% (p=0.0002).
• This approval marks the first time a combination of a HIF-2 alpha inhibitor (WELIREG) and a multi-targeted VEGFR-TKI (LENVIMA) has been approved for this specific patient population. It provides a new treatment option for patients with advanced ccRCC who have progressed after anti-PD-1/PD-L1 therapy, addressing a significant unmet need in a challenging disease setting.
• The prescribing information for WELIREG includes a boxed warning for embryo-fetal harm, and both drugs carry warnings for serious adverse reactions such as anemia, hypoxia, cardiac dysfunction, hypertension, and hepatotoxicity. Close monitoring for these adverse events and appropriate dose modifications or discontinuations are recommended to manage patient safety effectively.

Addressing Unmet Needs in Advanced ccRCC Post-PD-1/PD-L1 Therapy

Despite significant advances in immunotherapy and targeted therapy, advanced ccRCC remains a disease where durable responses are elusive for a substantial proportion of patients. The treatment landscape is complicated by intrinsic and acquired resistance mechanisms, inadequate predictive biomarkers, and molecular heterogeneity that current clinical risk stratification fails to capture.

• ICI resistance is prevalent and poorly understood. A substantial group of patients do not respond to immune checkpoint inhibitors, and few achieve long-term remission. Uniquely, ccRCC exhibits one of the highest levels of T cell infiltration across tumour types, yet high T cell infiltration does not correlate consistently with improved ICI outcomes — indicating that standard immunological markers behave differently in this cancer type.

• Conventional predictive biomarkers have limited utility. Tumour mutational burden in ccRCC is relatively low compared with other immunotherapy-responsive cancers and fails to predict ICI efficacy. PD-L1 status similarly shows limited predictive utility. This underscores the need for deeper exploration of the immunological mechanisms driving the antitumour immune response in ccRCC.

• Molecular heterogeneity is not captured by current risk stratification. Distinct transcriptomic subgroups exist within ccRCC — including an angiogenic subtype enriched in IMDC favourable-risk patients, characterised by high HIF pathway gene expression, frequent PBRM1 mutations, robust VEGF-TKI responsiveness, and comparatively lower benefit from immunotherapy. Current clinical risk stratification fails to capture this molecular heterogeneity, limiting optimal treatment selection.

• IO+TKI combinations have not demonstrated OS benefit in favourable-risk disease. A pooled analysis of four pivotal phase III trials (n = 839 favourable-risk patients) revealed no overall survival advantage for IO+TKI versus sunitinib monotherapy (hazard ratio 1.24; 95% CI 0.86–1.78), despite higher toxicity rates (71–82% Grade ≥ 3 adverse events vs. 63–72% with sunitinib) and substantially greater cost, raising concerns about overtreatment in this subgroup.

• VEGF-TKI resistance is common and mechanistically complex. Approximately 70% of patients who initially respond to VEGF-TKIs later develop drug resistance, with 30% innately resistant. Resistance mechanisms include restoration of alternative angiogenesis pathways and, in a subset of VEGFR-TKI-resistant patients, upregulation of PD-L1 expression via the mTOR signalling pathway — a finding with direct implications for sequencing ICI therapy after TKI failure.

• Treatment sequencing data remain insufficient. The lack of data on optimal sequencing of ICI and TKI regimens poses a challenge for physicians selecting both first-line and subsequent therapies, a problem expected to intensify as the treatment landscape grows more complex with emerging agents.

LITESPARK-011: Efficacy and Safety of Belzutifan Plus Lenvatinib

Several pivotal phase II and III trials have evaluated combination regimens in advanced clear cell renal cell carcinoma (ccRCC), spanning first-line and refractory settings. The studies below represent a cross-section of designs, from large randomised controlled trials to single-arm and basket studies, each contributing distinct evidence on efficacy and tolerability.

The knowledge base does not have sufficient information on this aspect.

The Novel Dual Mechanism of Belzutifan and Lenvatinib in ccRCC

The molecular pathogenesis of ccRCC is anchored in the inactivation of the von Hippel-Lindau (VHL) gene, located at chromosomal region 3p25, which occurs in the majority of both familial and sporadic cases — with VHL inactivation identified in up to 70% of sporadic RCC. Under normal conditions, the pVHL protein directs proteasomal degradation of hypoxia-inducible factors HIF-1 and HIF-2. Loss of functional pVHL results in constitutive stabilization and accumulation of these factors, driving expression of pro-tumorigenic targets including vascular endothelial growth factor (VEGF), platelet-derived growth factor, erythropoietin, carbonic anhydrase IX, and tumor growth factor alpha. Of the HIF subunits, HIF-2alpha appears more oncogenic than HIF-1alpha, activating pro-tumorigenic target genes while HIF-1alpha is more susceptible to proteasomal degradation in VHL-deficient RCC cells. This HIF-driven program promotes cell growth, proliferation, and angiogenesis, establishing the neoplastic phenotype characteristic of ccRCC. Downstream, HIF-related signaling routes — including the phosphatidylinositol 3-kinase–AKT–mTOR, RAS/RAF/MAP, and VEGF pathways — are activated and represent established therapeutic targets.

Beyond VHL, several adjacent tumor suppressor genes — BAP1, SETD2, and PBRM1 — are frequently co-lost and critically influence disease course. PBRM1 mutations arise early in ccRCC development, altering chromatin accessibility and acting as tumor co-initiators, while SETD2 mutations emerge later, exacerbating genomic instability and promoting metastasis. Co-mutation of PBRM1 and SETD2 correlates with increased tumor aggressiveness, poor prognosis, and higher metastatic potential. In the metastatic setting, whole exome sequencing has identified SETD2, PBRM1, APC, and VHL as the most frequently mutated genes, with recurrent somatic copy number variations at regions 3p25, 9p21, and 14q25 — early appearance of these CNVs may be associated with rapid clinical progression. Clonal evolution analyses further demonstrate that acquired resistance to tyrosine kinase inhibitor (TKI) therapy is driven by intra-tumor heterogeneity, with private mutations in FLT4, MTOR, ITGA5, SETD2, PBRM1, and BRCA1 detected at progression, underscoring the dynamic genomic landscape of advanced disease.

Metabolic reprogramming represents a third axis of ccRCC pathogenesis. Tumor cells preferentially engage aerobic glycolysis over oxidative phosphorylation — a shift enforced by the HIF-driven hypoxia response pathway. The mTOR signaling kinase, operating through complexes mTORC1 and mTORC2, integrates nutrient and energy sensing with regulation of cell growth, proliferation, and angiogenesis; dysregulation of this pathway is a hallmark of ccRCC. ECHS1, a key enzyme in fatty acid metabolism, is significantly downregulated in ccRCC tissues, and its overexpression suppresses RCC cell proliferation and migration through inhibition of mTOR pathway activation. In the context of TKI resistance, acceleration of glucose accumulation — measurable by FDG PET/CT — is dependent on mTOR signaling and correlates with disease progression, while mTOR inhibition suppresses this metabolic acceleration. The tumor immune microenvironment is also shaped by these molecular alterations: angiogenic factors promote immunosuppression by increasing regulatory T cells and myeloid-derived suppressor cells (MDSCs) while reducing mature dendritic cell and effector T-cell infiltration, and high HAVCR1 (KIM-1) expression is associated with increased CD8 and CD4 T-cell infiltration alongside upregulation of immune checkpoints PD-L1 (CD274) and CTLA4.

HIF-2α Inhibition Expands Role in Advanced ccRCC

The recent FDA approval of belzutifan plus lenvatinib for advanced clear cell renal cell carcinoma (ccRCC) patients who have progressed on PD-1/PD-L1 inhibitors marks a pivotal moment in the management of this aggressive disease. This combination, leveraging belzutifan's novel HIF-2α inhibition alongside lenvatinib's established VEGFR TKI activity, offers a compelling new therapeutic avenue where options are critically needed.

Based on the LITESPARK-011 trial, the combination demonstrated a significant improvement in progression-free survival (PFS) and objective response rate (ORR) compared to cabozantinib, a current standard. This positions belzutifan plus lenvatinib as a strong contender to become a new standard of care in the second-line setting, directly impacting treatment algorithms and intensifying competition among existing agents. The success of this combination further validates the therapeutic potential of targeting the HIF-2α pathway, which is a central driver of ccRCC biology, and supports the ongoing exploration of belzutifan in earlier lines of therapy and other combinations.

However, several factors warrant careful consideration:

• Toxicity Management: While the LITESPARK-011 trial reported a manageable safety profile, belzutifan monotherapy is known to cause adverse events such as anemia and fatigue. The integration into combination regimens, as seen in other trials, can lead to increased rates of grade ≥3 adverse events, necessitating vigilant patient monitoring and proactive management strategies.

• Overall Survival Data: The approval is primarily driven by robust PFS and ORR benefits. However, mature overall survival (OS) data, a critical measure of long-term patient benefit, are still pending. This will be a key area of focus for future updates.

• Evolving Treatment Landscape: The ccRCC treatment paradigm is rapidly evolving, with belzutifan itself being investigated in first-line triplet regimens (e.g., with pembrolizumab and lenvatinib) and in the adjuvant setting. Determining the optimal sequencing and placement of this newly approved combination within this dynamic landscape will be crucial for maximizing patient outcomes and requires further clinical evidence.

This approval underscores a strategic shift towards earlier and more diverse targeting of HIF-2α biology across the RCC disease continuum, from prevention to progression, promising expanded benefits for patients.