CCL17 and neoplasm: High expression of CCL17 in the TME of patients with gastric cancer (Mizukami et al., 2008) and Hodgkin’s lymphoma (Ishida et al., 2006) recruits large numbers of CD4+ Treg cells to infiltrate tumor tissues and inhibits CD8+ cytotoxic T lymphocyte function, resulting in local cellular immune suppression, and leading to a poor prognosis in patients.