Background: Tumor-associated macrophage kinases (TAMK) are expressed on tumor cells during malignant transformation. Inhibition of AXL and MERTK, members of the TAMK family, may lower the immune activation threshold and promote antitumor immunity. PF-07265807 (ARRY-067) is a small-molecule inhibitor of MERTK and AXL showing antitumor activity in preclinical models as monotherapy or combined with anti-programmed cell death protein 1 (anti-PD-1) antibodies (ab). Sasanlimab is an anti-PD-1 ab with acceptable safety profile being tested (300 mg SC Q4W, Phase 3) in non-muscle invasive bladder cancer. Axitinib is a VEGF inhibitor approved (single agent and combined with anti-PD-1 inhibitors) for advanced renal cell carcinoma (RCC). This first-in-human Phase 1, open-label, multi-center study (NCT04458259) will evaluate the safety, tolerability, pharmacokinetics, and preliminary antitumor activity of PF-07265807 in patients (pts) with advanced or metastatic solid tumors as a single agent and in combination with sasanlimab with or without axitinib. We describe here the dose escalation (Part 3) and dose expansion (Part 4) for the triplet combination of PF-07265807 + sasanlimab + axitinib. Methods: Eligible participants for the triplet cohorts are adult pts with confirmed unresectable advanced or metastatic clear cell RCC, with estimated creatinine clearance ≥30 mL/min and urinary protein <2+ or ≥2+ but 24-h urine protein:creatinine ratio <2 g/24 h. Pts for Part 4 need to have intermediate and poor risk RCC and no prior systemic therapy for metastatic disease. Other key eligibility criteria: measurable disease by RECIST 1.1 or non-measurable disease, ECOG PS 0–2, adequate bone marrow and liver function, and resolved acute effects of prior therapy. Each cycle is 21 days. Part 3 will determine the maximum tolerated dose/recommended phase 2 dose (MTD/RP2D) of PF-07265807 in triplet therapy using a Bayesian logistic regression model and the escalation with overdose control principle. After the MTD/RP2D is identified, Part 4 will further evaluate the safety and preliminary efficacy of PF-07265807 combined with sasanlimab and axitinib. Treatment with study drug will continue until disease progression, consent withdrawal, or unacceptable toxicity, whichever occurs first. Primary endpoints of Part 3 are incidence of dose-limiting toxicities, adverse events (AE), and laboratory (lab) abnormalities. For Part 4, the primary endpoints are objective response rate and complete response rate; secondary endpoints include disease control rate; time-to-event endpoints; AEs; lab abnormalities; concentrations of PF-07265807 and its metabolite, sasanlimab, and axitinib; and incidence and titer of anti-sasanlimab anti-drug antibodies response. The study started in late 2020 and is recruiting. Clinical trial information: NCT04458259.