PrimerX: A Bayesian Multistage Cohort Embedded Randomised Trial to Evaluate the Role of Deferred Local Therapy of the Primary Tumour in Combination with Immune Checkpoint Inhibitor-based First-line Therapy in Metastatic Renal Cell Carcinoma Patients.

Background: Historically, patients with metastatic renal cell carcinoma (mRCC) have been offered upfront cytoreductive nephrectomy (CN) followed by systemic therapy. Currently, CN is no longer the standard of care (SOC) based on the randomised phase 3 CARMENA study performed in the vascular endothelial growth factor receptor tyrosine kinase inhibitor era. With the advent of immune checkpoint inhibitor (ICI) combination therapy in first line, the role of CN needs to be reassessed. There is indirect evidence from small retrospective series that deferred CN after ICI combination therapy may lead to better outcomes. To reassess the role of CN, we designed PrimerX, a randomised controlled trial following the Trial within Cohorts (TwiCs) study design. The primary objective of this study is to re-evaluate the benefit of deferred local treatment in the current era of immunotherapy. Study design: This PrimerX study has been designed as a TwiCs study within the Dutch Prospective Renal Cell Carcinoma (PRO-RCC) cohort. The PRO-RCC cohort includes patients with mRCC and nonmetastatic RCC, and has been set up for prospective collection of long-term clinical data and as an infrastructure for initiating TwiCs studies. The PrimerX TwiCs trial follows a Bayesian adaptive multistage design to allow for early discontinuation due to futility or efficacy. PrimerX has appropriate ethics approval and is registered at clinical.trials.gov (NCT05941169). End points: The primary clinical endpoint is overall survival, defined as the time from randomisation to death from any cause. The secondary endpoint is the objective response rate within the primary tumour prior to local therapy, as assessed by a computed tomography scan. Patients and methods: A maximum of 700 patients with synchronous mRCC and absence of progression at metastatic sites following at least 6 mo of standard first-line ICI combination therapy will be assigned randomly to receive local treatment of the primary tumour (experimental arm) or SOC (control arm). The experimental intervention consists of (partial) CN, any form of ablative local therapy, or magnetic resonance imaging guided ablative stereotactic radiotherapy, performed within 6 mo and 1.5 yr after the start of systemic treatment.