In addition, TAM-derived prostaglandin E2 (PGE2), IL-10, and indoleamine 2,3-dioxygenase play important roles in the induction of Tregs and TAM-derived CCL17, CCL18, and CCL22 are chemotactic factors for Tregs [40], which results in the suppression of T cells in the tumor microenvironment. Here, CCL18 is linked to neoplasm.