Background <p>Tinurilimab is a humanized immunoglobulin G subclass 2 antibody that blocks carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6), an immune checkpoint regulator that is overexpressed in several tumor types.</p> Objectives <p>This phase I study evaluated the safety, tolerability, pharmacokinetics, pharmacodynamics, and tumor response profile of tinurilimab in patients with advanced solid tumors with a described expression of CEACAM6.</p> Patients and Methods <p>In this first-in-human, dose-escalation and dose-expansion study, tinurilimab was administered as a 1-h intravenous infusion in 21-day cycles at a starting dose of 2.5&#xa0;mg, with a planned escalation up to 1800&#xa0;mg. Following observation of treatment toxicity (cytokine release syndrome in one patient and neutropenia in all patients treated at 30&#xa0;mg), a premedication regimen was initiated that included dexamethasone 8&#xa0;mg before and after dosing. Thirty patients received treatment across six dosing cohorts (2.5–100 mg with or without dexamethasone).</p> Results <p>The maximum tolerated dose was not determined, as the study was terminated due to an unfavorable benefit/risk assessment. All 30 patients (100%) treated with tinurilimab experienced at least one treatment-emergent adverse event of any grade, most commonly fatigue (36.7%), infusion-related reaction (30.0%), and neutropenia (26.7%). The most common grade&#xa0;≥&#xa0;3 treatment-related adverse events were neutropenia (23.3%), followed by febrile neutropenia, cytokine release syndrome, increased hepatic enzymes, decreased lymphocyte count, hypophosphatemia, lactic acidosis, and acute kidney injury (3.3% each). No patients reported an objective response.</p> Conclusions <p>Following study termination, the clinical development program for tinurilimab was discontinued permanently.</p> Clinical trial registration <p><a href="https://clinicaltrials.gov/study/NCT03596372">www.clinicaltrials.gov</a>, NCT03596372.</p>