Of note, levels of circulating sPD-L1 seem to be heterogeneous in cancer patients; specifically, our results showed that levels of sPD-L1 detected in mesothelioma patients were lower compared to those reported by other studies in cancer patients of different tumor histotypes, such as gastric cancer, B-cell lymphoma, and multiple myeloma [27,38,39]. This evidence concerns the gene SPDL1 and plasma cell myeloma.