Although the roles of endothelial cells in cancer have primarily been considered to be related to tumor perfusion, the emerging appreciation of "angiocrine" regulation adds stromal regulatory capabilities to the expanding list of endothelial functions in tumors. We posit that an understanding of the state-dependent paracrine regulatory paradigms established in vascular disease and repair will be critical for a deep understanding of tumor biology, as endothelial cells regulate diverse processes in all vascularized tissues. Here, we outline the historical developments that led to the appreciation of the paracrine regulatory functions of endothelial cells, summarize classical views of blood vessels and stroma in cancer, and attempt to merge these ideas to include the stromal regulatory endothelial cell as a critical regulator of cancer. The notion of the endothelial cell as a biochemical regulator of cancer state in constant dynamic balance with its tumor could impact diagnosis, prognosis, and treatment of cancer. Such concepts might well explain the mixed results from antiangiogenic cancer therapeutics and how certain drugs that improve vascular health correlate with improved cancer prognosis.