Background: Most RCCs contain clear cell histology; the remainder of cases are summarized as nccRCC. nccRCC is a heterogeneous group of tumors and, with advanced metastases, survival is uniformly worse than with clear cell RCC (ccRCC) because of the aggressiveness of these cancers and a lack of effective systemic treatment options. Because data are limited for patients with nccRCC, the role of various agents in the treatment of nccRCC is poorly defined and there is no standard of care; treatment guidelines recommend clinical trials as preferred strategy. Inhibition of the PD-1/PD-L1 pathway is an effective treatment option for nccRCC, and pembrolizumab monotherapy has shown efficacy with an acceptable safety profile as first-line treatment. The VEGF TKI lenvatinib has also shown efficacy with a tolerable safety profile as combination therapy with everolimus for nccRCC. Also, in the phase 3 KEYNOTE-581 study (NCT02811861), the combination of lenvatinib + pembrolizumab as first-line therapy showed antitumor activity in patients with metastatic ccRCC, suggesting this combination might be an excellent therapeutic option for nccRCC. The phase 2, open-label, single-arm, KEYNOTE-B61 study (NCT04704219) is being conducted to evaluate pembrolizumab in combination with lenvatinib as first-line treatment for nccRCC. Methods: Patients with centrally confirmed nccRCC, locally advanced/metastatic measurable disease per RECIST v1.1 per blinded independent central review (BICR), no prior systemic therapy for nccRCC, and KPS score ≥70 will be enrolled. Approximately 152 patients will receive pembrolizumab 400 mg every 6 weeks and lenvatinib 20 mg once daily. Pembrolizumab treatment will continue for up to approximately 2 years or until a discontinuation criterion is met (disease progression, unacceptable toxicity, or withdrawal of consent); lenvatinib treatment can continue beyond 2 years or until one of the same discontinuation criterion is met. Participants who discontinue one of the treatments can continue to receive the other treatment as monotherapy. A second-course treatment phase is available for patients who meet specific criteria. CT/MRI will be performed at 12 weeks from the start of treatment, every 6 weeks until week 54, and every 12 weeks thereafter. Adverse events will be monitored throughout the study and graded using CTCAE, version 5.0, guidelines. The primary end point is objective response rate based on RECIST v1.1 per BICR. Secondary efficacy end points for this study are clinical benefit rate, disease control rate, duration of response, progression-free survival, overall survival, and safety. Tertiary/exploratory end points are biomarker analysis and association with clinical response/disease etiopathogenesis. Clinical trial information: NCT04704219