Background: First-line combination chemotherapy with pembrolizumab followed by maintenance pembrolizumab is the standard of care treatment for patients with metastatic sqNSCLC. This was established by the phase III KEYNOTE-407 trial, which demonstrated a median progression-free survival (PFS) of 6.4 months in the experimental arm. Despite these advances, there remains a need to continue to improve upon survival outcomes for these patients. Cabozantinib is a small-molecule inhibitor of multiple tyrosine kinsases including MET, VEGFRs, AXL, RET, and ROS, which are receptors involved in tumor cell-proliferation, angiogenesis, and immune cell regulation. Preclinical studies have demonstrated the ability of cabozantinib to modulate both adaptive and innate immune cells and to exhibit synergistic activity when used in combination with immune checkpoint inhibitors. We hypothesize that cabozantinib in combination with pembrolizumab in the maintenance phase of first-line treatment of metastatic sqNSCLC will prolong median PFS with a tolerable toxicity profile. Methods: LUNG-IST 127 is a pilot phase II, single-arm clinical trial of maintenance cabozantinib in combination with pembrolizumab for patients with metastatic sqNSCLC who achieved disease control following standard 1L induction therapy with chemotherapy and pembrolizumab. Thirty-six patients will be enrolled at 2 US sites to receive first-line induction therapy with carboplatin, nab-paclitaxel or paclitaxel, and pembrolizumab for four cycles. After induction therapy, those who have achieved disease control based on re-staging imaging will continue onto maintenance therapy with cabozantinib 40mg PO daily in combination with pembrolizumab 200mg IV every 3 weeks. The primary endpoint is PFS estimated by Kaplan-Meier methods with associated 95% confidence intervals. Based on an exploratory power analysis using an elevated one-sided alpha level of 0.40, we hypothesize that the proposed therapy will prolong median PFS from 6.4 to 9 months. Key secondary endpoints include overall survival (OS), overall response rate (ORR), and characterizing the safety and tolerability of cabozantinib in combination with pembrolizumab. Quality of life will also be measured with the EORTC QLQ-C30. Correlative endpoints include characterizing cfDNA from biofluids and assessing the change in circulating immune cells in different phases of treatment in association with PFS and OS. This trial would be the first to address whether there is clinical benefit in utilizing combination cabozantinib and pembrolizumab in the maintenance phase of treatment in metastatic sqNSCLC. Clinical trial information: NCT05613413.