Highlights
Sustained Survival Benefit
With a median follow-up of 19.8 months, serplulimab plus chemotherapy demonstrated a median overall survival of 15.8 months compared to 11.1 months for chemotherapy alone, representing a 38 percent reduction in the risk of death.
Novel Proteomic Signature
A 15-protein signature derived from serum proteome profiling was identified as a significant predictor of both overall survival and progression-free survival in patients receiving serplulimab.
Genomic Predictive Markers
Mutations in the retinoblastoma-1 (RB1) gene and members of the Notch signaling pathway were associated with improved clinical outcomes, offering a potential path toward personalized immunotherapy in SCLC.
Prognostic Value of Blood Markers
Baseline neutrophil-to-lymphocyte ratio (NLR) and lactate dehydrogenase (LDH) levels were confirmed as independent prognostic factors for patients with extensive-stage small-cell lung cancer.
Introduction: The Shifting Landscape of ES-SCLC Treatment
Extensive-stage small-cell lung cancer (ES-SCLC) has long been characterized by its aggressive clinical course, rapid doubling time, and early development of widespread metastases. For decades, the therapeutic ceiling for this disease remained stagnant, with platinum-based chemotherapy serving as the standard of care but offering limited long-term survival. The advent of immune checkpoint inhibitors, specifically those targeting the programmed death 1 (PD-1) and programmed death ligand 1 (PD-L1) axis, has finally broken this plateau.
Serplulimab, a novel recombinant humanized anti-PD-1 monoclonal antibody, was investigated in the ASTRUM-005 trial to address the unmet need for more effective first-line interventions. Initial reports from this trial established a significant survival advantage. However, the durability of this benefit and the identification of which patients derive the most clinical utility from this combination remained critical questions. The updated results of ASTRUM-005, alongside a comprehensive exploratory biomarker analysis, provide essential data for clinicians managing this challenging malignancy.
Study Design and Methodology
ASTRUM-005 was a randomized, double-blind, placebo-controlled Phase 3 clinical trial. The study enrolled 585 treatment-naive patients with ES-SCLC across multiple international sites. Participants were randomized in a 2:1 ratio to receive either serplulimab (4.5 mg/kg) or a matching placebo intravenously every three weeks. Both groups received standard chemotherapy consisting of carboplatin (AUC 5) and etoposide (100 mg/m2 on days 1–3 of each cycle).
The primary endpoint was overall survival (OS). Secondary endpoints included progression-free survival (PFS), objective response rate (ORR), and duration of response (DOR). Beyond clinical efficacy, the study investigators conducted an extensive exploratory analysis. This included genomic profiling via next-generation sequencing to identify somatic mutations and quantitative serum proteome profiling to distinguish differentially expressed proteins (DEPs) between responders and non-responders. A 15-protein signature was subsequently constructed using regression analysis to evaluate its predictive and prognostic value.
Updated Efficacy: Sustained Survival Benefits
The updated analysis, conducted after a median follow-up of nearly 20 months, reinforces the robust efficacy of serplulimab. In the intent-to-treat population, the median OS reached 15.8 months in the serplulimab group compared to 11.1 months in the placebo group. The hazard ratio (HR) for death was 0.62 (95% CI: 0.50–0.76), maintaining statistical significance (P < 0.001).
Notably, the survival curves showed early and sustained separation. The 24-month OS rate was significantly higher in the serplulimab arm (33.5 percent) than in the placebo arm (15.8 percent). This doubling of the two-year survival rate is a clinically meaningful milestone for a disease where long-term survival was previously rare. Progression-free survival also favored the serplulimab arm, with a median of 5.8 months versus 4.3 months (HR 0.46; 95% CI: 0.38–0.57). The objective response rate was 80.2 percent for the serplulimab combination compared to 70.4 percent for chemotherapy alone, with a more durable response observed in the immunotherapy group.
Biomarker Analysis: Decoding the Responders
One of the most significant contributions of the updated ASTRUM-005 report is the identification of biomarkers that may help clinicians predict which patients are most likely to benefit from the addition of serplulimab.
The 15-Protein Signature
Through quantitative serum proteome profiling, researchers identified 181 proteins that were differentially expressed between those who responded to serplulimab and those who did not. From this pool, a 15-protein signature was developed. Patients with a high protein signature score experienced significantly longer OS and PFS. This proteomic approach is particularly promising because serum samples are non-invasive and can be collected longitudinally, unlike tissue biopsies which are often difficult to obtain in SCLC due to the small size of samples and the presence of necrosis.
Genomic Markers: RB1 and Notch
Genomic analysis revealed that mutations in the retinoblastoma-1 (RB1) gene, a hallmark tumor suppressor in SCLC, were associated with improved outcomes in the serplulimab group. While RB1 loss is common in SCLC, specific mutational profiles appear to sensitize the tumor to PD-1 inhibition. Similarly, mutations in the Notch signaling pathway, which regulates neuroendocrine differentiation in the lung, were linked to enhanced ORR and survival. These findings suggest that the genomic landscape of the tumor influences the immune microenvironment and the subsequent efficacy of serplulimab.
Hematological and Biochemical Prognosticators
The study also validated the prognostic value of baseline neutrophil-to-lymphocyte ratio (NLR) and lactate dehydrogenase (LDH) levels. High baseline NLR and elevated LDH were independent indicators of poor prognosis. These markers reflect the systemic inflammatory state and tumor burden, respectively, and remain easily accessible tools for risk stratification in routine clinical practice.
Safety and Tolerability
The safety profile of serplulimab plus chemotherapy remained consistent with previous reports and was generally manageable. Grade 3 or higher treatment-emergent adverse events (TEAEs) occurred in 82.3 percent of the serplulimab group and 80.1 percent of the placebo group, suggesting that most high-grade toxicities were attributable to the chemotherapy backbone rather than the immunotherapy. Immune-related adverse events (irAEs) were more frequent in the serplulimab arm but were mostly low-grade and consistent with the known safety profile of PD-1 inhibitors.
Expert Commentary: Clinical Implications
The ASTRUM-005 trial results solidify serplulimab’s position as a potent first-line option for ES-SCLC. The median OS of 15.8 months is among the highest reported in Phase 3 trials for this population. From a biological perspective, the discovery of the 15-protein signature and the predictive value of RB1 and Notch mutations provide a foundation for future precision oncology strategies.
However, it is important to note that while these biomarkers are promising, they require external validation in independent cohorts before they can be integrated into standard diagnostic protocols. Furthermore, the study population primarily consisted of Asian patients, and while the results are compelling, ongoing global studies will further clarify the generalizability of these findings across diverse ethnic backgrounds.
Conclusion
The updated results from the ASTRUM-005 randomized clinical trial confirm that first-line serplulimab plus chemotherapy provides a sustained and clinically significant survival benefit for patients with extensive-stage small-cell lung cancer. The identification of proteomic and genomic biomarkers marks a significant step toward moving beyond a one-size-fits-all approach in SCLC. As we continue to refine our understanding of the molecular drivers of response, serplulimab stands out as a critical component of the modern therapeutic armamentarium against this aggressive disease.
Funding and Registration
This study was funded by Shanghai Henlius Biotech, Inc. The trial is registered with ClinicalTrials.gov, number NCT04063111.
References
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2. Horn L, Mansfield AS, Szczęsna A, et al. First-line atezolizumab plus chemotherapy in extensive-stage small-cell lung cancer. N Engl J Med. 2018;379(23):2220-2229.
3. Paz-Ares L, Dwyer-Lindgren L, Huang J, et al. Durvalumab plus platinum-etoposide in first-line treatment of extensive-stage small-cell lung cancer: 3-year overall survival update from CASPIAN. ESMO Open. 2022;7(2):100408.
