Petosemtamab Doubles Survival Signal but Full Data and Precedent Still Missing

Genmab's Petosemtamab Combination Achieves Dual Primary Endpoints in First-Line HNSCC

Genmab announced positive topline results from the global Phase 3 LiGeR-HN1 trial, evaluating petosemtamab in combination with pembrolizumab against pembrolizumab alone for first-line PD-L1 positive recurrent/metastatic head and neck squamous cell carcinoma (HNSCC). The study met its dual primary endpoints, demonstrating a statistically significant and clinically meaningful improvement in overall survival (OS) and objective response rate (ORR). The petosemtamab combination reduced the risk of death by 50% (OS: HR 0.50; p<0.0001) and showed a significantly higher ORR (odds ratio 3.17; p<0.0001), regardless of HPV status. The safety profile was consistent with known profiles of individual agents, with no new signals. Genmab plans to engage global regulatory authorities and present full results at a future medical meeting.

• The LiGeR-HN1 trial demonstrated a statistically significant and clinically meaningful improvement in overall survival (OS) for the petosemtamab and pembrolizumab combination. Patients experienced a 50% reduction in the risk of death compared to pembrolizumab alone, with a Hazard Ratio of 0.50 (95% CI, 0.37, 0.67) and a p-value of <0.0001, highlighting a substantial survival advantage for patients with first-line PD-L1 positive recurrent/metastatic HNSCC.
• Beyond survival, the combination therapy also achieved a significantly higher objective response rate (ORR), a co-primary endpoint. The odds ratio for ORR was 3.17 (95% CI, 2.06, 4.89) with a p-value of <0.0001, indicating that patients treated with petosemtamab plus pembrolizumab were more than three times as likely to experience a tumor response. This robust response rate further supports the clinical efficacy of the novel bispecific antibody.
• The safety profile of petosemtamab in combination with pembrolizumab was generally well tolerated and consistent with previously reported profiles of the individual agents, with no new safety signals identified. These positive topline results position the combination as a potential new chemotherapy-free treatment option. Genmab intends to engage global regulatory authorities and submit the comprehensive data for presentation at an upcoming medical conference, aiming to bring this transformative therapy to patients.

Addressing the Unmet Needs in Recurrent/Metastatic HNSCC

Only a subset of head and neck cancer patients benefit from immune checkpoint inhibitors, although the introduction of immune checkpoint inhibitors to oncological care has transformed the management of head and neck squamous cell carcinoma, offering improved outcomes. Pembrolizumab was approved as a first-line treatment, with or without chemotherapy, based on tumor and immune cell percentage of programmed-death ligand 1 (PD-L1).

• Limited predictive value and heterogeneity of PD-L1 and related biomarkers. PD-L1 expression assessed by immunohistochemistry is the single most clinically relevant biomarker predicting response to PD-1-blocking antibodies, yet reliable biomarkers predicting response to PD-1 blockade remain limited. In 40 patients with recurrent or metastatic head and neck squamous cell carcinoma treated with nivolumab or pembrolizumab monotherapy, PD-L1 expression and densities of CD4⁺, CD8⁺, and FoxP3⁺ T cells were not associated with response, with objective response rate was 18%, with median overall survival of 13 months and progression-free survival of 3 months. PD-L1 status was 64% (21/33) concordant between the initial and recurrent lesions using a CPS 1 threshold and 67% (22/33) concordant using a CPS 20 threshold, with 43% (15/35) and 66% (23/35) concordance for the IFN-γ and TLS signature scores, respectively. Immunotherapy regimens may be personalized by tumor biomarker, including PD-L1 content, tumor mutational burden, and microsatellite instability, and patients with positive PD-L1 expression experienced improved overall survival when treated with PD-1 or PD-L1 inhibitors, particularly those with high PD-L1 expression, while PD-L1 expression did not significantly affect progression-free survival.

• Lack of standardized biomarker methods and regimen sequencing. Further clinical trials are needed to refine biomarker-driven protocols and standardize pathological methods to guide combined regimen timing, sequencing, and deescalation. Translation of mRNA expression to a clinically relevant cut off or threshold is challenging due to variability between assays and the detection of different analytes, and threshold optimisation for %TCmRNA and mean dots/tumour cell results in high specificity to IHC PD-L1 classification, but only moderate sensitivity. Gaps remain for protocols using immunotherapy to reverse oral premalignant lesions, particularly high-risk leukoplakias.

• Efficacy-toxicity trade-offs in first-line selection. The standard-of-care first-line therapy for recurrent or metastatic head and neck squamous cell carcinoma is pembrolizumab monotherapy for patients with a PD-L1 combined positive score (CPS)≥1 or pembrolizumab combined with platinum and 5-fluorouracil for patients with any PD-L1 status. Addition of chemotherapy to pembrolizumab increases the response rate but also toxicity and is preferred for patients with good performance status and significant tumor and symptom burden.

• Immune-related adverse events and supportive-care gaps. Guidelines are also needed to standardize the role of dental evaluation and care before, during, and after immunotherapy, specifically in regard to oral immune-related adverse events and their impact on cancer recurrence. Reported events include acute pneumothorax-sometimes bilateral-can occur shortly after PD-1 inhibition, particularly in patients with subpleural metastatic disease, and metachronous type 1 diabetes mellitus and isolated adrenocorticotropic hormone deficiency associated with pembrolizumab monotherapy with Combined Positive Score of 100 achieving complete remission.

LiGeR-HN1: Design and Positive Outcomes in First-Line HNSCC

First-line and previously treated recurrent or metastatic head and neck squamous cell carcinoma have been defined by two randomised phase 3 trials of pembrolizumab stratified by programmed death ligand 1 expression. KEYNOTE-048 evaluated pembrolizumab with or without chemotherapy in untreated locally incurable disease, while KEYNOTE-040 evaluated pembrolizumab versus investigator-choice chemotherapy in platinum-progressed disease.

Petosemtamab's Dual-Targeting MoA and Expanding Pipeline

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Reshaping the First-Line HNSCC Treatment Paradigm

In recurrent or metastatic head and neck squamous cell carcinoma (R/M HNSCC), anti-PD-1 monotherapy improved overall survival (OS) versus standard of care (SoC) chemotherapy with cetuximab, docetaxel, or methotrexate. Treatment with nivolumab led to improved OS with a hazards ratio (HR) of 0.70 (95%CI 0.51-0.96; p = 0.01) and pembrolizumab with HR of 0.80 (95%CI 0.65-0.98, p = 0.0161), with OS observed in the control SoC arms of 6.9 months median in KEYNOTE 040 versus 5.1 months in CheckMate 141. Pooled analyses showed anti-PD1/PD-L1 monotherapy provided statistically significant overall survival benefit with hazard ratio (95% confidence interval) = 0.79 [0.70-0.90] and a 37% lower risk of death (OR = 0.63, 95% CI = 0.51-0.78, I = 18%, p ≤ 0.0001), with no significant difference in progression-free survival (hazard ratio [95% confidence interval] = 0.96 [0.85-1.09]) and less treatment-related adverse events than standard of care, including a 77% lower risk of any-grade TRAEs (OR = 0.23, 95% CI = 0.18-0.29, I = 90%, p ≤ 0.00001). In KEYNOTE-040, objective response rate (ORR) for pembrolizumab versus SOC was 26.2 versus 8.5% for TPS ≥ 50%, 28.1 versus 7.7% for CPS ≥ 50, 10.6 versus 11.6% for TPS < 50%, and 10.0 versus 12.0% for CPS < 50, with CPS ≥ 50 appearing equivalent to TPS ≥ 50% for predicting ORR, overall survival, and progression-free survival.

PD-1 inhibitor plus chemotherapy significantly prolonged progression-free survival (hazard ratio [HR] 0.66, 95% CI 0.40-0.93, p < 0.001) and OS (HR 0.73, 95% CI 0.60-0.86, p < 0.001) compared with SoC in first-line treatment for R/M-SCCHN in three phase 3 RCTs (KEYNOTE-048, CAPTAIN-1st, and JUPITER-02; n = 1120) with pembrolizumab, camrelizumab and toripalimab, with no statistical differences in ORR (odds ratio [OR] 1.26; 95% CI 0.97-1.64, p = 0.086), grade 3 or higher AEs (OR 0.77, 95% CI 0.50-1.17, p = 0.221), and treatment-related deaths (OR 1.34, 95% CI 0.60-2.98, p = 0.470). For PD-L1 combined positive score (CPS) ≥1 first-line R/M HNSCC, enfortumab vedotin (EV) (1.25 mg/kg IV) on days 1, 8 and pembrolizumab (200 mg IV) on day 1 in 21-day cycles in EV-202 cohort 9 (NCT04225117) in 41 patients, of whom 39.0% had PD-L1 CPS 1-19 and 61.0% had CPS ≥20, showed investigator-assessed confirmed objective response rate (cORR) of 39.0% (95% CI: 24.2-55.5), complete response rate of 9.8%, duration of response (DOR) not estimable with estimated 6-month DOR rate of 81.7% (95% CI: 42.0-95.4), and median PFS of 5.1 months (95% CI: 3.5-NE) at median follow-up for OS of 11.0 months, with grade 3 treatment-related adverse events in 41.5% of patients, most commonly maculopapular rash (7.3%).

Durvalumab with or without tremelimumab did not improve OS versus SoC (cetuximab, a taxane, methotrexate, or a fluoropyrimidine) in the randomized, open-label phase III EAGLE study in R/M HNSCC patients assigned to durvalumab (n = 240) (10 mg/kg every 2 weeks [q2w]), durvalumab plus tremelimumab (n = 247) (durvalumab 20 mg/kg q4w plus tremelimumab 1 mg/kg q4w × 4, then durvalumab 10 mg/kg q2w), or SoC (n = 249), with OS for durvalumab versus SoC [hazard ratio (HR): 0.88; 95% confidence interval (CI): 0.72-1.08; P = 0.20] and durvalumab plus tremelimumab versus SoC (HR: 1.04; 95% CI: 0.85-1.26; P = 0.76), 12-month survival rates (95% CI) of 37.0% (30.9-43.1), 30.4% (24.7-36.3), and 30.5% (24.7-36.4), and grade ≥3 trAE rates of 10.1%, 16.3%, and 24.2%, respectively. Heavily pretreated patients in early-phase trials of novel immunotherapy agents (158 patients, median [range] age 60.7 [25.7-84.6] years, median of 3 prior lines (range, 0-8 prior lines), 126 patients (79.7%) with prior ICI exposure, 91 of 153 patients (59.5%) with human papillomavirus-positive tumors, PD-L1 combined positive score of at least 1 in 67 of 87 patients (77.0%)) had overall response rate of 7.7% (12 patients), clinical benefit rate (complete or partial response or stable disease lasting ≥6 months) of 16.1% (25 patients), median progression-free survival of 2.3 months (95% CI, 2.0-2.9 months) and median overall survival of 8.3 months (95% CI, 7.2-11.0 months), with treatment-related adverse effects in 85 patients (53.8%), including grade 3 or higher events in 23 patients (14.6%), while bispecific antibodies were associated with improved clinical benefit (odds ratio, 1.95; 95% CI, 1.23-4.15) and PIK3CA alterations with reduced benefit (odds ratio, 0.03; 95% CI, 0.00-0.51). Other investigational combinations included eftilagimod alpha plus pembrolizumab as second-line therapy with objective response rate of 29.7%, including 13.5% complete responders, and intralesional SD-101 plus pembrolizumab with objective response rate of 24% including 2 complete and 10 partial responses, median duration of response of 7.0 [95% confidence interval (CI): 2.1-11.1] months, and progression-free and overall survival at 9 months of 19.0% (95% CI: 9.1-31.7) and 64.7% (95% CI: 45.3-78.7), respectively, with 12 patients with grade ≥3 treatment-related adverse events (24%).

Bispecific Breakthrough: Reshaping First-Line HNSCC Treatment

The recent positive topline results from the LiGeR-HN1 trial mark a significant moment for patients battling recurrent or metastatic head and neck squamous cell carcinoma (HNSCC). This patient population faces a particularly grim prognosis, with limited effective treatment options, especially once their disease progresses or becomes resistant to existing therapies like anti-PD-1 agents. The current standard of care often falls short, underscoring a critical unmet need for more potent and durable treatments.

Enter petosemtamab, a novel bispecific antibody designed to target both epidermal growth factor receptor (EGFR) and leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5). This dual-targeting approach is particularly compelling because EGFR is a well-known oncogenic driver in HNSCC, while LGR5 is upregulated and plays a role in potentiating the WNT/β-catenin signaling pathway, which stimulates cancer stem cell proliferation and self-renewal. By also enhancing antibody-dependent cellular cytotoxicity (ADCC), petosemtamab offers a multi-pronged attack against the tumor. The LiGeR-HN1 trial's success, demonstrating a 50% reduction in the risk of death and a significantly higher objective response rate when combined with pembrolizumab compared to pembrolizumab alone, suggests a powerful new therapeutic strategy. This outcome, regardless of HPV status, could fundamentally shift the treatment paradigm for first-line PD-L1 positive r/m HNSCC.

Strategically, this validates the bispecific antibody platform and its potential to address complex oncogenic pathways. It positions the combination as a strong contender for a new standard of care, potentially impacting the competitive landscape. However, several considerations remain. While the safety profile was consistent with individual agents, detailed adverse event data will be essential for clinical integration. Furthermore, navigating regulatory approvals and securing favorable market access and reimbursement will be critical steps, especially given the potential for premium pricing associated with innovative combination therapies. The long-term durability of these impressive responses will also be key to establishing sustained clinical value. This development not only offers hope for HNSCC patients but also reinforces the promise of sophisticated, multi-targeted immunotherapies.