Evaluation of RC48-ADC in Combination with PRaG Regimen: An Open-Label, Prospective, Multicentre Study Assessing Efficacy and Safety for Advanced Refractory HER2-Expressing Solid Tumors (PRaG3.0 Study Protocol).

IntroductionThis study aims to investigate the effectiveness and safety of combining the antibody-drug conjugate (ADC) disitamab vedotin (RC48) with the established PRaG regimen (PD-1 inhibitor, Radiotherapy, and GM-CSF) for treating HER2-expressing (IHC 3+, 2+, or 1+) advanced solid tumors. This novel PRaG3.0 regimen is hypothesized to leverage the tumor radiosensitizing and immunogenic cell death properties of ADCs to amplify the synergistic antitumor effects of radioimmunotherapy, offering a potential paradigm for pan-cancer therapy.MethodsThis study is a prospective, single-arm, open-label, multi-center clinical trial. Patients enrolled have confirmed HER2-expressing solid tumors (IHC 3+, 2+, or 1+) that have progressed after standard treatment or were intolerant to it. Patients received RC48 (2 mg/kg) via intravenous injection on day 1, followed by subcutaneous GM-CSF at 200 µg from days 3 to 7 and interleukin-2 (IL-2) at 2 million IU from days 8 to 12. Radiotherapy was initiated on day 3, targeting one lesion with hypofractionated radiotherapy (2-3 fractions of 5 or 8 Gy). PD-1/PD-L1 antibodies were administered within one week after completing radiotherapy. Treatment was repeated every three weeks, and if there were no target lesions, radiotherapy could be discontinued, with RC48 given for at least six cycles. After achieving a complete tumor response, maintenance therapy with PD-1/PD-L1 antibodies continued until disease progression or intolerable toxicity occurred. The primary endpoint was the objective response rate (ORR).ResultsThe study is currently in the recruitment phase (Registration No: NCT05115500). The primary endpoint is the objective response rate (ORR). Secondary endpoints include progression-free survival (PFS), overall survival (OS), disease control rate (DCR), safety, and QoL. Planned enrollment is 62 patients.ConclusionThe PRaG3.0 protocol represents an innovative approach combining ADC therapy with radioimmunotherapy to address HER2-expressing cancers, including those with HER2-low expression. If successful, this regimen could establish a highly effective combination strategy.