Ris-Rez Phase 3 OS Win in SCLC: First-in-Class Validation With Undisclosed Magnitude and China-First Regulatory Lag

GSK and Hansoh's B7-H3 ADC Achieves Phase 3 Overall Survival Win

GSK and Hansoh Pharmaceutical's experimental B7-H3-targeted antibody-drug conjugate (ADC), risvutatug rezetecan (ris-rez), achieved its primary endpoint of overall survival in the Phase 3 ARTEMIS-008 trial for patients with advanced small cell lung cancer (SCLC) in China. This pivotal success marks the first positive Phase 3 overall survival data for a B7-H3-targeted ADC in any tumor type. The trial, which randomized approximately 460 patients to receive either ris-rez or chemotherapy, also demonstrated consistent benefit across key secondary endpoints like progression-free survival, with no new safety signals. Hansoh plans to use these data for a regulatory submission in China, while GSK, holding exclusive global rights outside Greater China from a $1.7 billion deal, will continue advancing the ADC across multiple tumor types globally.

• The Phase 3 ARTEMIS-008 trial, conducted by Hansoh Pharmaceutical in China, met its primary endpoint of overall survival (OS) for risvutatug rezetecan (ris-rez) in patients with advanced small cell lung cancer (SCLC). This statistically significant improvement over standard of care represents a significant milestone as the first positive Phase 3 OS data for a B7-H3-targeted antibody-drug conjugate in any tumor type.
• Beyond the primary endpoint, ris-rez demonstrated consistent benefits across key secondary endpoints, including progression-free survival (PFS). The open-label study, involving approximately 460 patients, also reported no new safety signals, indicating a safety profile consistent with prior findings for the B7-H3-targeted ADC.
• Following these positive results, Hansoh Pharmaceutical intends to prepare a regulatory submission in China. GSK, which secured exclusive global rights to ris-rez outside of China, Hong Kong, Macau, and Taiwan in a deal valued up to $1.7 billion in December 2023, plans to further advance the ADC across various tumor types, including a global Phase 3 SCLC study expected to read out next year.

ARTEMIS-008 Delivers First Phase 3 OS Win for B7-H3 ADC

The DeLLphi-301 phase 2 study evaluated tarlatamab 10 mg — a DLL3-directed bispecific T-cell engager — against real-world third-line or later comparator therapies in previously treated SCLC (n=97 vs. n=184). Following propensity score weighting, tarlatamab demonstrated a hazard ratio of 0.45 (95% CI: 0.30–0.68) for overall survival, 0.61 (95% CI: 0.43–0.90) for progression-free survival, and an odds ratio of 2.80 (95% CI: 1.44–5.83) for objective response rate, suggesting a clinically meaningful benefit over available comparators. Building on this, the DeLLphi-303 phase 1b study assessed tarlatamab 10 mg every two weeks in combination with atezolizumab or durvalumab as first-line maintenance therapy in 88 patients, yielding a median OS of 25.3 months (95% CI: 20.3–not estimable) at a median follow-up of 18.4 months. The most common grade 3–4 adverse events were hyponatraemia (10%), anaemia (8%), and neutropenia (7%), while cytokine release syndrome (CRS) was the most frequent serious adverse event (24%), with no treatment-related deaths reported.

Real-world safety data from a retrospective Moffitt Cancer Center study of 40 patients treated with tarlatamab between May 2024 and February 2025 revealed substantially higher toxicity rates than those observed in clinical trials. Among patients who did not receive prophylactic tocilizumab (n=30), 53.3% developed CRS and 23.3% developed immune effector cell-associated neurotoxicity syndrome (ICANS) following Cycle 1 Day 1, with grade ≥3 severity in 10% for each; three patients discontinued therapy due to severe CRS/ICANS, including two deaths. In contrast, among the ten patients who received prophylactic tocilizumab, only one developed grade 2 CRS and none developed ICANS. Elevated LDH and liver metastasis were identified as independent predictors of CRS, while diabetes and cardiovascular disease were independently associated with ICANS. Separately, the NEJ045A phase 2 trial examined durvalumab combined with carboplatin and etoposide, followed by durvalumab maintenance, in 57 treatment-naive extensive-stage SCLC patients with poor performance status (PS 2–3). The regimen met its primary tolerability endpoint: 67% of PS 2 patients and 50% of PS 3 patients completed induction therapy, with one-year survival rates of 50.0% and 18.2%, respectively. However, grade ≥3 adverse events occurred in 93% of patients and 21% discontinued due to toxicity.

In the relapsed setting, a study of nab-paclitaxel plus anlotinib (ANNAB) versus nab-paclitaxel alone as second-line therapy in 48 patients demonstrated superiority across all efficacy endpoints: median PFS 6.0 vs. 4.7 months (p=0.0004), ORR 37.5% vs. 8.3% (p=0.0363), and median OS 10.0 vs. 7.3 months (p<0.0001), with no significant difference in adverse events between arms. The maintenance-setting NCT04363255 phase 2 trial of toripalimab (240 mg every 3 weeks) plus anlotinib (12 mg on days 1–14 of each 21-day cycle) in 20 ES-SCLC patients who achieved disease control after first-line platinum-etoposide reported a median PFS of 8.18 months during the maintenance phase and a median OS of 23.05 months, with a manageable safety profile. Mechanistically, anlotinib was found to promote dose-dependent PD-L1 upregulation and Notch signalling activation, with post-treatment reductions in serum neuroendocrine markers NSE and ProGRP correlating significantly with improved survival outcomes.

B7-H3: An Emerging Target for Small Cell Lung Cancer

B7-H3 (CD276) has emerged as one of the most promising targets in SCLC owing to its uniform expression across all major molecular subtypes — a critical advantage in a disease defined by significant transcriptional heterogeneity. Next-generation antibody-drug conjugates directed against B7-H3 are under active clinical investigation, with early Phase I data for SYS6043 demonstrating robust response rates in SCLC as well as other solid tumors including ovarian and breast cancers. Concurrently, CAR-T cell platforms targeting CD276 are being refined to address a key mechanistic liability: T-cell activation and CAR signaling induces CD276 expression on the CAR-T cells themselves, precipitating CD276-dependent fratricide that limits both expansion and antitumor activity. The Adapter CAR-T (AdCAR-T) platform circumvents this through novel Fab-based adapter molecules (AMs) that enable CAR-T expansion in the absence of CD276 engagement, with intermittent AM dosing preserving functional persistence in vivo. This activity is further enhanced by incorporating activation-induced, AM-remote-controlled IL-18 secretion into the AdCAR-T construct. Complementary work with non-viral c-JUN+B7-H3 CAR T cells — engineered via CRISPR-Cas9 knock-in at the TRAC locus — demonstrates enhanced killing of SCLC cells with low antigen density, with GMP-scale clinical manufacturing confirmed as feasible.

Beyond B7-H3, several additional surface antigens and intracellular targets are attracting substantial investigational interest. DLL3, a direct ASCL1 transcriptional target most highly expressed in ASCL1-positive tumors, was validated by the 2024 approval of the DLL3×CD3 bispecific antibody tarlatamab; next-generation DLL3-directed ADCs, including BL-M14D1, have shown robust early Phase I response rates. CD56-targeting ADC DXC006 and next-generation ADCs directed at TROP2 and SEZ6 are similarly under investigation. At the kinase level, PLK1 inhibitor onvansertib is in Phase II evaluation for relapsed SCLC, inducing G2/M arrest through impairment of cell cycle transition, while Aurora kinase B inhibitor AZD2811 (nanoparticle-formulated, 500 mg IV on Day 1 of 21-day cycles) has demonstrated tolerability in Phase I dose-escalation. TNIK inhibition represents a molecularly nuanced approach, showing preferential activity in c-MYC-high SCLC via c-MYC downregulation, with additional antitumor effects in POU2F3-expressing tumors through SOX9 suppression; combination with anti-PD-L1 produced superior efficacy and reduced immunosuppressive cell infiltration in immunocompetent in vivo models.

Deeper mechanistic research is also illuminating novel immune-metabolic and epigenetic vulnerabilities. In ASCL1-high (SCLC-A) tumors — an immunologically cold subtype — elevated glycolytic activity driven by LDHA suppresses MHC-I expression through lactate-mediated histone H4K5 lactylation and subsequent PRC2-dependent silencing of H2Db/H2Kb and B2M; pharmacological LDHA inhibition with FX11 restores MHC-I surface expression and, in combination with anti-PD-1, synergistically inhibits tumor growth. UHRF1, a chromatin effector of RB1/E2F signaling, promotes SCLC growth and metastasis across subtypes while reinforcing neuroendocrine lineage programs via PRC2 interaction; its loss derepresses DNA-methylation-silenced tumor antigens including MAGE-A4 and increases CD8 T cell and myeloid infiltration. The TEM8 receptor (encoded by ANTXR1), exploited by the oncolytic virus SVV-01, offers a strategy to convert immunologically cold SCLC into T cell-inflamed tumors more responsive to immune checkpoint inhibitors, with a Phase 1 trial of SVV-01 plus ICI currently underway. Collectively, these advances underscore the imperative for biomarker-driven patient stratification — integrating molecular subtyping (ASCL1, NEUROD1, POU2F3, YAP1), immune profiling, and emerging epigenetic and metabolic signatures — to optimize therapeutic selection across this heterogeneous disease.

Overcoming Limitations in Advanced Small Cell Lung Cancer Treatment

Small cell lung cancer (SCLC) remains one of the most therapeutically intractable malignancies, characterized by early metastasis, rapid relapse, and a prognosis that has changed little despite decades of research. The disease's genomic and immunological architecture presents compounding barriers that have frustrated the translation of novel agents into durable clinical benefit. Understanding these limitations is essential context for evaluating emerging treatment strategies.

• High mutational burden with limited druggable targets: Despite a genomically complex landscape marked by substantial intratumoral and intertumoral heterogeneity, SCLC harbors few readily actionable gene aberrations, constraining the development of precision oncology approaches analogous to those established in NSCLC.

• Chemotherapy responses are transient and followed by profound resistance: Although most patients with SCLC respond to initial chemotherapy, these responses are short-lived. At relapse, tumors exhibit high resistance to subsequently available therapies, and multiple clinical trials have failed to demonstrate meaningful survival improvements in this setting.

• Immunologically cold tumor microenvironment: SCLC tumors are more immunodeficient than NSCLC, with low PD-L1 expression, downregulation of MHC molecules, and regulatory chemokine suppression, collectively enabling immune escape and limiting the efficacy of checkpoint inhibitor-based strategies.

• Transcriptional plasticity and intratumor heterogeneity drive treatment resistance: Increasingly recognized as a central mechanism of therapeutic failure, transcriptional plasticity allows SCLC cells to adopt alternative molecular subtypes under treatment pressure, undermining both targeted and immune-based approaches.

• Biomarker deficiency and biopsy inaccessibility: Validated predictive biomarkers for patient selection and response monitoring in SCLC remain inconsistent or absent across most novel therapeutic classes, including PARP inhibitors. Compounding this, acquisition of tumor biopsies — particularly at relapse — is a substantial clinical and logistical challenge.

• Class-specific toxicities constrain novel targeted agents: Emerging modalities such as DLL3-directed bispecific T-cell engagers (e.g., tarlatamab) are balanced by class-specific toxicities including cytokine release syndrome and neurotoxicity, while efficacy may be further attenuated by antigen density variability, microenvironmental suppression, and the sequencing of prior therapies.

• Etoposide-associated limitations persist: Challenges with topoisomerase II inhibitors — particularly etoposide, a backbone of SCLC chemotherapy — include drug resistance, systemic toxicity, and limited efficacy at relapse, underscoring the need for improved drug delivery systems and combination strategies to enhance the therapeutic window.

Pivotal SCLC Data Validates B7-H3 ADC Strategy

The recent announcement regarding risvutatug rezetecan (ris-rez), a B7-H3-targeted antibody-drug conjugate (ADC), marks a significant moment in oncology, particularly for the challenging landscape of small cell lung cancer (SCLC). Achieving the primary endpoint of overall survival in a Phase 3 trial is the gold standard for demonstrating clinical benefit, and for ris-rez, this success not only offers a new therapeutic avenue for patients with advanced SCLC but also validates B7-H3 as a compelling target for ADC development.

This breakthrough is particularly impactful because SCLC is an aggressive disease with limited treatment options, especially in advanced stages. The positive data suggests ris-rez could significantly improve patient outcomes, potentially establishing a new standard of care. For GSK, holding exclusive global rights outside Greater China, this positions them to introduce a first-in-class B7-H3 ADC to major markets worldwide, leveraging the clinical success achieved by Hansoh in China. This strategic collaboration underscores the growing trend of global partnerships to accelerate drug development and market access.

However, as with any novel therapy, important considerations remain. Earlier Phase 1a/b data for HS-20093 (ris-rez) highlighted a safety profile that included significant grade ≥3 treatment-related adverse events such as decreased neutrophil and white blood cell counts, anemia, and notably, interstitial lung disease (ILD) in 3.4% of patients, with adverse events leading to death in 3.8%. These safety signals, particularly ILD, will require careful management and monitoring in broader clinical practice and could influence prescribing patterns. Furthermore, while the China-based Phase 3 trial is a strong indicator of efficacy, global regulatory bodies may seek additional data to confirm generalizability across diverse patient populations. The dynamic oncology landscape also means that while ris-rez is currently a frontrunner, continuous innovation and competitive pressures will shape its long-term market trajectory.