A phase II clinical trial has demonstrated that combining two immunotherapy agents significantly improves outcomes for patients with advanced cutaneous squamous cell carcinoma (cSCC), offering new hope for treating this aggressive form of skin cancer. The Alliance for Clinical Trials in Oncology study met its primary endpoint, showing that the combination of avelumab and cetuximab improved progression-free survival compared to avelumab alone.
Trial Design and Patient Population
The Alliance A091802 trial enrolled 60 patients with advanced cSCC across the United States from 2019 to 2023, with 57 patients evaluable for analysis. The median age of participants was 72 years, with the majority being white (96.5%) and male (91.2%). All patients were HIV-negative, and 75.4% expressed PD-L1. Most tumors (84.2%) originated in the head or neck region, and 47.1% of patients had distant metastases.
Patients were randomized to receive either avelumab monotherapy every two weeks or the combination of avelumab plus cetuximab, also administered every two weeks. The trial included a crossover design, allowing patients who progressed on avelumab alone to switch to combination therapy, enabling evaluation of efficacy in both frontline and immunotherapy-refractory settings.
Significant Survival Improvement
The combination therapy achieved the primary endpoint with remarkable results. The median progression-free survival was 11.1 months (95% confidence interval: 7.6–not reached) in the avelumab plus cetuximab group compared to 3.0 months (95% CI: 2.7-13.6) in the avelumab alone group, representing a hazard ratio of 0.48 (95% CI: 0.23–0.97, p = 0.018).
"These results show that combining immune checkpoint inhibition targeting the PD-1: PD-L1 pathway with avelumab plus EGFR-targeted IgG1 monoclonal antibody cetuximab can provide meaningful clinical benefit compared to avelumab alone for patients with advanced cSCC," said Dan Zandberg, MD, principal investigator and Director of Head and Neck and Thyroid Cancer Disease Sections at UPMC Hillman Cancer Center.
Nine patients in the avelumab monotherapy arm crossed over to the combination group, achieving a median progression-free survival of 11.3 months (5.8-not reached) after crossover. The median overall survival was not reached (25.2–not reached) in the combination group compared to 35.8 months (18.6–not reached) in the avelumab group, with a hazard ratio of 0.78 (0.34–1.80, p = 0.279). The confirmed objective response rate was 27.6% in the combination group versus 21.4% in the avelumab alone group.
Mechanism of Action and Rationale
The therapeutic rationale combines two distinct immunological approaches. Avelumab is an immune checkpoint inhibitor that targets PD-L1, releasing the brakes on T cell activity against cancer cells. Cetuximab is a monoclonal antibody targeting EGFR (epidermal growth factor receptor), which activates natural killer cells and dendritic cells while also triggering antibody-dependent cellular cytotoxicity (ADCC).
"The rationale for the combination is that avelumab and other anti-PD-1/PD-L1 therapies have been shown to take the foot off the brake of the immune system, while cetuximab is pressing on the gas pedal — trying to work together to make the immune system go faster and attack the tumor," explained Zandberg. "What's exciting is that in this trial the efficacy of the combination suggests that the two drugs were synergistic, rather than just additive."
Safety Profile
Treatment-related adverse events occurred in 93% of patients receiving the combination therapy compared to 78.6% of those receiving avelumab alone. Grade 3 or higher adverse events were observed in 48.3% of combination patients versus 21.5% of avelumab monotherapy patients. The most common serious side effects in the combination group were rash (20.7%) and infusion-related reactions (20.7%). Importantly, there were no treatment-related deaths or unexpected toxicities.
Clinical Context and Future Implications
Cutaneous squamous cell carcinoma represents one of the most common cancers in the United States, with approximately 700,000 to 1 million new cases diagnosed annually. While most cases are treatable when detected early, over 12,500 cases progress to nodal or distant metastases each year, contributing to an estimated 2,000 to 8,000 deaths annually.
Although approved immune checkpoint inhibitors cemiplimab and pembrolizumab have advanced the treatment landscape, many patients still experience disease progression. This trial represents the first completed prospective randomized comparison of cetuximab plus PD-1/PD-L1 pathway blockade versus pathway blockade alone in cSCC.
"These findings highlight the potential benefits of combining cetuximab with an anti-PD-1/PD-L1 therapy and points to the importance of additional clinical trials combining either standard of care pembrolizumab or cemiplimab with cetuximab as a potential way to improve patient outcomes in advanced cSCC," noted Zandberg.
The crossover results suggest that continuing immunotherapy while adding cetuximab could be more beneficial than switching to cetuximab or chemotherapy alone when patients fail initial immunotherapy treatment. This finding could inform future treatment sequencing strategies for patients with advanced cSCC.
