GAS6 and neoplasm: It is already known that Gas6 is expressed not only by tumor cells but also by endothelial cells, fibroblasts, vascular smooth muscle cells, and infiltrating immune cells,28 and tumor cells are stimulated via paracrine as well as autocrine fashion by Gas6, which also is found in serum.10 It also is assumed that paracrine-derived Gas6 incorporation into tumor cells represses tumoral Gas6 expression per se, resulting in downregulation of Gas6 mRNA expression.