Challenges and the Evolving Landscape of Assessing Blood-Based PD-L1 Expression as a Biomarker for Anti-PD-(L)1 Immunotherapy

Abstract

While promising, PD-L1 expression on tumor tissues as assessed by immunohisto chemisthas been shown to be an imperfect biomarker that only applies to a limited number of cance whereas many patients with PD-L1-negative tumors still respond to anti-PD-(L)1 immunotherap Recent studies using patient blood samples to assess immunotherapeutic responsiveness suggesa promising approach to the identification of novel and/or improved biomarkers for anti-PD-(Limmunotherapy. In this review, we discuss the advances in our evolving understanding of thregulation and function of PD-L1 expression, which is the foundation for developing blood-basePD-L1 as a biomarker for anti-PD-(L)1 immunotherapy. We further discuss current knowledge anclinical study results for biomarker identification using PD-L1 expression on tumor and immuncells, exosomes, and soluble forms of PD-L1 in the peripheral blood. Finally, we discuss key chlenges for the successful development of the potential use of blood-based PD-L1 as a biomarker fanti-PD-(L)1 immunotherapy.