Disclosed is a method and test kit to diagnose tumorigenicity or the presence of tumor cells in a patient by detecting the level of FBLN-3 expression or biological activity in the patient. Also disclosed are methods to identify regulators of tumor cell growth, motility and/or invasion, by identifying regulators of FBLN-3 expression or activity. Methods to identify anti-angiogenic and pro-angiogenic agents are also described, wherein such factors regulate the expression and/or activity of FBLN-3. Finally, the present invention relates to therapeutic methods and reagents for the inhibition of tumor growth and development and/or for the inhibition or promotion of angiogenesis, using FBLN-3, homologues and analogs thereof, and agents that modulate the expression and/or activity of FBLN-3.