ARG1 and neoplasm: Multiple studies have suggested that arginase-1 expression of tumor cells is largely absent in other important tumor types, such as renal cell carcinomas [8,25], ductal adenocarcinoma of the pancreas [8,21], gastric adenocarcinoma [25], esophageal adenocarcinoma [25], adenocarcinoma of the lung [25], and in lobular breast cancer [25].