Co-expression of thymidine phosphorylase and heme oxygenase-1 in macrophages in human malignant vertical growth melanomas

Expression of thymidine phosphorylase (TP) is often associated with tumor angiogenesis and/or prognosis in patients. Further, infiltration of macrophages is closely correlated with the depth of tumor and angiogenesis in melanomas. In this study, we examined the expression of TP and an activated macrophage-specific enzyme, heme oxygenase-1 (HO-1), involved in malignancy in 22 cases with melanomas. TP was strongly expressed not only in CD68-positive macrophages in and around tumors, but also in S100 protein-positive melanoma cells, fibroblasts and keratinocytes. By contrast, HO-1 was specifically expressed in macrophages, but only slightly in melanoma cells and other cell types in the stroma of melanomas. We thus observed apparent co-expression of TP and HO-1 in macrophages infiltrating in the late stage of malignant melanomas. There appeared increasing numbers of TP-positive cells in Clark level IV and V melanoma compared with Clark level I (in situ) melanoma, and there was also a close correlation between numbers of TP-positive cells and HO-1-positive cells. Both TP- and HO-1-positive macrophages could be observed in the stroma in and around tumors in vertical growth melanomas.