Based on this background, in this study we investigated whether Valproic acid (VPA), a class I/IIa HDAC inhibitor that has been shown to inhibit HDAC2 [12], could influence the expression and the acetylation of PD-L1 and whether acetylation could affect its interaction with molecules such as TRAPPC4 and its localization on cell surface of pancreatic cancer cells. This evidence concerns the gene HDAC9 and pancreatic neoplasm.