ISG15 and carcinoma: We limit our discussion of the roles of ISG15 in cancers of nondigestive organs primarily to tumors that arise from epithelial tissues, such as carcinomas of the breast, lung, and urinary bladder, because these are likely relevant to carcinomas of the esophagous, stomach, intestine, colon, liver, and pancreas, which are more common in digestive organs than tumors arising from other tissue types [26].