8559 Background: Pembrolizumab plus platinum-based chemotherapy is a standard first-line treatment for previously untreated advanced squamous non-small cell lung cancer (NSCLC) based on the KEYNOTE-407 trial. Ubenimex, an oral CD13/aminopeptidase inhibitor, has immunostimulatory and antitumor activity. We conducted a phase II trial to assess the safety and efficacy of ubenimex in combination with pembrolizumab, nab-paclitaxel, and carboplatin in patients with previously untreated advanced squamo