Long-Term Survival Data Highlights Rakuten Medical Photoimmunotherapy Combination
Four out of five complete responders in a Phase 1b/2 combination study of Rakuten Medical’s ASP-1929 photoimmunotherapy combined with pembrolizumab remain alive more than five years after treatment, according to long-term follow-up data presented as an e-poster at the European Society for Medical Oncology (ESMO) 2026 in Madrid. That longevity contrasts sharply with historical outcomes for pembrolizumab monotherapy in recurrent or metastatic head and neck squamous cell carcinoma (r/m HNSCC), where median overall survival typically hovers around eight months.
The updated analysis extended median follow-up from 31.7 months to 53.1 months across 17 efficacy-evaluable patients. Median overall survival reached 28.2 months, with 35.3% of patients still alive at the four-year mark. Among the five patients achieving a complete response, four survived with follow-up ranging past 42 months and, in some cases, past 60 months. Median duration of response hit 44.3 months at data cutoff, and four responders required no subsequent anticancer therapy after stopping study treatment.
Small subgroup sizes limit definitive trial results
The trial enrolled 19 patients, of whom 17 were evaluable. Exploratory subgroup cuts examining human papillomavirus (HPV) status, programmed death-ligand 1 (PD-L1) combined positive score (CPS) expression, and tumor size showed broadly consistent results without generating new safety signals. However, small subgroup numbers mean these patterns remain suggestive rather than definitive. Rakuten Medical acknowledges these limitations, framing the results as support for continued clinical investigation rather than absolute proof of benefit.
The therapy relies on cetuximab sarotalocan (RM-1929), an antibody-dye conjugate targeting epidermal growth factor receptor (EGFR) on cancer cells. When activated by non-thermal red light at a wavelength of 690 nanometers, the drug induces selective cell necrosis and immune activation.
Phase 3 study tests therapy as first-line treatment
To establish definitive efficacy, Rakuten Medical initiated the global Phase 3 ASP-1929-381 study (NCT06699212). This trial is testing the combination as a first-line therapy for locoregionally recurrent HNSCC, enrolling approximately 400 to 412 patients in a population distinct from the previously studied r/m setting. The current first-line standard relies heavily on pembrolizumab and platinum-based regimens, leaving the Phase 3 trial to determine whether photoimmunotherapy adds durable tumor control on top of existing care.
Rakuten Medical has held conditional marketing approval for the drug in Japan since September 2020. For the U.S. market, the company targets a Biologics License Application (BLA) submission in 2028, contingent upon the success of the Phase 3 trial. Enrollment pace and interim analysis timing serve as the next concrete markers for the program.
Frequently Asked Questions About the ASP-1929 Trial
What is the regulatory status of ASP-1929 outside Japan?
ASP-1929 remains strictly investigational outside Japan, where it has held conditional marketing approval since September 2020. The ongoing global Phase 3 ASP-1929-381 study aims to support regulatory submissions in other regions, including a targeted U.S. BLA filing in 2028.
How does photoimmunotherapy work mechanically?
The treatment uses cetuximab sarotalocan, an antibody-dye conjugate that binds to EGFR on the surface of cancer cells. Upon exposure to non-thermal red light at 690 nm, the drug is activated to induce selective cell necrosis and trigger localized immune activation.
What patient population does the Phase 3 trial evaluate?
The global Phase 3 ASP-1929-381 trial evaluates approximately 400 to 412 patients with locoregionally recurrent HNSCC as a first-line therapy. This represents a narrower patient population than the recurrent or metastatic setting examined in the Phase 1b/2 study.
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