On October 20, 2025, IO Biotech (Nasdaq: IOBT) presented a proffered paper at the Melanoma and Other Skin Tumors session of the 2025 European Society for Medical Oncology (ESMO) Congress in Berlin, detailing the final Phase 3 IOB‑013/KN‑D18 results for its lead vaccine, Cylembio (IO102‑IO103), in combination with Merck’s KEYTRUDA® (pembrolizumab). The presentation expanded upon the topline data released in August 2025 and provided a more granular analysis of the primary progression‑free survival (PFS) endpoint.
The updated data show a median PFS of 19.4 months for the Cylembio plus pembrolizumab arm versus 11.0 months for pembrolizumab alone, yielding a hazard ratio of 0.77 (95 % CI 0.58–1.00, p = 0.0558). Subgroup analyses consistently favored the combination across PD‑L1–negative tumors (16.6 vs 3.0 months, HR 0.54), BRAF V600‑mutated tumors (HR 0.60), and patients with elevated LDH (HR 0.60). A post‑hoc analysis excluding patients previously exposed to anti‑PD‑1 therapy in neoadjuvant or adjuvant settings showed a median PFS of 24.8 months versus 11.0 months (HR 0.74, 95 % CI 0.56–0.98).
Safety outcomes were comparable to the pembrolizumab‑only arm, with no increase in immune‑mediated adverse events (34.0 % vs 38.4 %) or grade ≥ 3 treatment‑related events (14.5 % vs 15.6 %). Local vaccine‑related injection‑site reactions occurred in 56 % of patients in the exploratory arm and were predominantly mild (grade 1/2). Immune‑profiling data confirmed expanded IDO1‑ and PD‑L1‑specific T‑cell responses in the vaccine arm, supporting the proposed mechanism of action.
In addition to the Phase 3 data, IO Biotech presented final results from its Phase 2 basket trial (IOB‑022/KN‑D38) evaluating Cylembio plus pembrolizumab in first‑line non‑small‑cell lung cancer (NSCLC) and squamous cell carcinoma of the head and neck (SCCHN). Among 49 efficacy‑evaluable patients, median PFS was 8.1 months in the NSCLC cohort and 7.0 months in the SCCHN cohort, with durable responses and 18‑month overall survival rates exceeding 70 % in both groups. Safety remained consistent with the monotherapy profile, and no new safety signals were identified.
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