A phase 3 trial of IMC-F106C (PRAME x CD3) plus nivolumab versus standard nivolumab regimens in HLA-A*02:01+ patients with previously untreated advanced melanoma (PRISM-MEL-301).

TPS9602 Background: Current standard of care in newly diagnosed patients with metastatic cutaneous melanoma (CM) include anti-PD1 as monotherapy or in combination with other immune checkpoint inhibitors (ICI). However, most patients will eventually progress and the 5-year survival rate remains low, necessitating new therapies with novel mechanisms of action to combine with anti-PD1. T cell receptor (TCR) bispecifics have shown overall survival (OS) benefit with tebentafusp (gp100 ´ CD3) in a phase (Ph) 3 trial in metastatic uveal melanoma 1. IMC-F106C is the first TCR bispecific protein targeting CD3 and PRAME (PRAME ´ CD3), redirecting T cells towards cancer cells presenting a PRAME peptide on the cell surface by HLA-A*02:01 proteins. PRAME is expressed in the vast majority of melanoma. In an ongoing Ph 1 study (NCT04262466), IMC-F106C monotherapy was well tolerated and demonstrated evidence of durable clinical activity in heavily pre-treated, advanced melanoma patients, including those who progressed on prior ICI and targeted therapy 2. Two doses, 40 mcg and 160 mcg, were selected for further study based on exposure response modeling. Safety of combination TCR bispecifics with ICI has been demonstrated in the ongoing IMC-F106C Ph 1 study and in a prior study of tebentafusp + ICI 3. Combining IMC-F106C with the anti-PD1 ICI nivolumab has the potential to improve progression free survival (PFS), OS, and response rate (RR). Methods: PRISM-MEL-301 is a randomized, global, open-label, Ph 3 study in previously untreated HLA-A*02:01+ patients with unresectable or metastatic non-uveal melanoma; up to 10% of patients can have a diagnosis of mucosal, acral, or other non-CM melanoma. The first 90 patients will be randomized 1:1:1 to receive IMC-F106C 40 mcg + nivolumab (Arm A), IMC-F106C 160 mcg + nivolumab (Arm B), or a nivolumab regimen (Arm C) from which a final IMC-F106C dose (Arm A or B) will be selected. Subsequently, approximately 590 additional patients will be randomized to Arm (A or B) vs. control Arm C, either nivolumab monotherapy or nivolumab + relatlimab, dependent on the country. Randomization will be stratified by 1) American Joint Committee on Cancer (8th Edition) M stage with lactate dehydrogenase (LDH; M0 or M1 with normal LDH vs M1 with elevated LDH); 2) prior anti-PDL1 adjuvant therapy (yes vs no); and 3) BRAF V600 mutation status (positive vs negative). Primary endpoint is PFS per RECIST 1.1 by blinded independent central review. Secondary endpoints include OS, ORR, and safety. Enrollment is ongoing globally. Clinical trial registration: NCT06112314 Nathan et al. N Engl J Med 2021; 385:1196 Hamid et al. Ann Oncol 2022; 33 (Supp7): S875 Hamid et al. J Immunother Cancer 2023; 11(6): e006747. Clinical trial information: NCT06112314 .