Increased number of arginase 1-positive cells in the stroma of carcinomas compared to precursor lesions and nonneoplastic tissues

Arginase 1 (Arg1) is involved in dampening the response of antitumor T lymphocytes. Arg1 expression has been reported in a variety of cancer cell lines and tumor-associated myeloid-derived cells. However, its examination in situ in tumor microenvironment is poorly investigated. We examined the Arg1-positive cells in tumor microenvironment of gastric carcinomas (GCs), colorectal carcinomas (CRCs) and prostate carcinomas (PCs), and analyzed their clinicopathological significance. Immunohistochemical staining for Arg1 was done in 60 GCs, 38 gastric adenomas, 40 CRCs, 10 colonic adenomas, 36 PCs, and 15 benign prostatic hyperplasia (BPH). Arg1 expression was predominantly localized in tumor microenvironment and the stroma of nonneoplastic tissues. Cells with Arg1 expression were mostly leukocytes, morphologically resembling polymorphonuclear neutrophils, and showed CD15 expression. Arg1 expression was focally expressed in cancer cells of 6 PCs, but not in those of GCs and CRCs. Arg1-positive cells were significantly more infiltrated in tumors than adenomas and nonneoplastic tissues, such as BPH, intestinal metaplasia and adjacent tissues. There were no significant findings between them and clinicopathological parameters, except for the relationship to gender and tumor differentiation in CRCs. These findings suggest that Arg1-positive cells in tumor microenvironment is involved in the occurrence of GCs, CRCs, and PCs. More expansive studies are necessary to better elucidate their clinicopathological significance in carcinomas.