Compositions and methods for targeted delivery to and detection of sites of neovascular growth, including tumor vasculature, are provided. Compositions include polypeptides conjugated to or complexed with a bioactive compound, wherein the polypeptide is capable of binding to an OEC or a circulating progenitor thereof. Methods for identifying additional polypeptides with the same binding characteristics are further provided. Methods for targeted delivery of a bioactive compound to a site of neovascular growth are provided in which polypeptides capable of binding OECs or progenitors thereof are conjugated to or complexed with the bioactive compound and administered to a subject in need thereof. Methods for detecting neovascular growth are also provided, wherein the polypeptides conjugated to or complexed with a detectable label are administered to a subject and the label is detected.
