ISG15 and neoplasm: Importantly, since ISG15 is also expressed by TAMs in the tumor microenvironment (TME)22, the META data set [consisting of four published PDAC gene expression studies (n = 108) including data sets with tumor cellularity >35% (GSE32688) or micro-dissected samples (GSE15471)] and the Moffitt series [which applies a virtual microdissection approach to identify distinct tumor- and stroma-specific signatures] allowed for the identification of genes preferentially overexpressed in tumor epithelia.