Tumor immunotherapy has become a standard of care for treating various cancers, with immune checkpoint inhibitors targeting the PD-L1/PD-1 axis proving particularly effective. While PD-L1 expression on tumor cells is a predictive biomarker for therapeutic response, emerging evidence highlights the importance of PD-L1 expression on myeloid cells, such as monocytes and dendritic cells (DCs), in shaping the tumor microenvironment and influencing the success of checkpoint blockade.