NODAL and neoplasm: TGFβ and Nodal are members of the TGFβ superfamily and are discussed in section The TGFβ signaling pathway below, while VEGFR-2 is discussed in section The vascular endothelial growth factor receptor-2 (VEGFR-2)/Flk-1 pathway on the basis of its more well-established role in affecting the tumor microenvironment.