Randomized, Open-Label, Phase III Study of Tilsotolimod in Combination With Ipilimumab Versus Ipilimumab Alone in Patients With Advanced Refractory Melanoma (ILLUMINATE-301).

Purpose: There are limited treatment options for advanced melanoma that have progressed during or after immune checkpoint inhibitor therapy. Intratumoral (IT) immunotherapy may improve tumor-specific immune activation by promoting local tumor antigen presentation while avoiding systemic toxicities. The phase 3 ILLUMINATE-301 study (ClinicalTrials.gov identifier: NCT03445533) evaluated tilsotolimod, a Toll-like receptor-9 agonist, with or without ipilimumab in patients with anti-PD-1 advanced refractory melanoma.

Methods: Patients with unresectable stage III-IV melanoma that progressed during or after anti-PD-1 therapy were randomly assigned 1:1 to receive 24 weeks of tilsotolimod plus ipilimumab or 10 weeks of ipilimumab alone. Nine IT injections of tilsotolimod were administered to a single designated lesion over 24 weeks. Intravenous ipilimumab 3 mg/kg was administered once every 3 weeks from week 2 in the tilsotolimod arm and week 1 in the ipilimumab arm. The primary end point was efficacy measured using objective response rate (ORR; independent review) and overall survival (OS).

Results: A total of 481 patients received tilsotolimod plus ipilimumab (n = 238) or ipilimumab alone (n = 243). ORRs were 8.8% in the tilsotolimod arm and 8.6% in the ipilimumab arm, with disease control rates of 34.5% and 27.2%, respectively. Median OS was 11.6 months in the tilsotolimod arm and 10 months in the ipilimumab arm (hazard ratio, 0.96 [95% CI, 0.77 to 1.19]; P = .7). Grade ≥3 treatment-emergent adverse events occurred in 61.1% and 55.5% of patients in the tilsotolimod and ipilimumab arms, respectively.

Conclusion: Combining IT tilsotolimod with ipilimumab did not significantly improve the ORR or OS compared with ipilimumab alone in patients with anti-PD-1 advanced refractory melanoma.