GREM1 and melanoma: The production of transforming growth factor β1 (TGF-β1) and previously identified efficacy-associated factors5, melanoma inhibitory activity (MIA), Dickkopf WNT signaling pathway inhibitor 1 (DKK1), endothelial cell-specific molecule 1 (ESM1), and gremlin 1 (GREM1) confirmed by enzyme-linked immunosorbent assay (ELISA) (Fig. 2g).