To then elucidate the role of this special form of PD-L1 in the tumor microenvironment, the authors injected wild-type (WT), Rab27a null, and PD-L1 null TRAMP-C2 cells into the flanks of C57BL6/J syngeneic mice, and, after excluding the key factors of exosomes production, found that Exo-PD-L1 promoted tumor progression. This evidence concerns the gene RAB27A and neoplasm.