Abstract CT208: Tebotelimab, a PD-1/LAG-3 bispecific antibody, in patients with untreated, unresectable, recurrent or metastatic, mucosal melanoma: An open-label, single-arm, Phase 1 study

Background: Immune checkpoint inhibitors (CPIs) targeting PD-(L)1 have become a standard of care for untreated, advanced melanoma, but demonstrated limited efficacy in mucosal melanoma. Tebotelimab, also known as MGD013, is a PD-1/LAG-3 bispecific tetravalent DART® molecule with synergistic antitumor activity shown in preclinical studies. We conducted an open-label, single-arm, multi-cohort phase 1 study (NCT04653038) to assess the efficacy and safety of tebotelimab in melanoma patients (pts) including those with CPI-naïve mucosal melanoma. Methods: The CPI-naïve cohort of this study enrolled pts with unresectable, recurrent or metastatic, mucosal or acral melanoma who had received no systemic therapy. Tebotelimab 600 mg was administered intravenously once every two weeks. The primary endpoint was overall response rate (ORR) assessed by independent radiologic review committee (IRC) per RECIST v1.1 in the efficacy analysis set consisting of pts who received ≥1 dose of tebotelimab. A post-hoc sensitivity analysis was conducted in the IRC-response evaluable set consisting of pts with IRC-assessed target lesions in the efficacy analysis set who received ≥1 post-baseline tumor assessment by IRC or died within 13 weeks after first dose. Results are reported for mucosal melanoma. Results: At data cut-off (January 19, 2022), 25 pts with mucosal melanoma were enrolled (median age, 61 years; male, 40%; ECOG 1, 40%; TNM Stage IV, 92%; metastatic, 80%). LAG-3 expression level was ≥1% in seven (28%),