IL6 and neoplasm: However, the induced secretion of IL-6 by PGE2 (Fig. 4B), as well as the basal levels of IL-6 secretion in these tissue derived fibroblasts (Fig. S4B) both failed to associate with the tumor promoting abilities of these fibroblasts in vivo (Fig. 2A), or their ability to secrete PGE2 in vitro (Fig. 2C).