Abstract: A method for assessing prognosis in a subject having a breast tumor comprises determining the level of expression of at least one Notch receptor gene, Notch ligand gene or Notch signaling target gene. A method of treating a subject suffering from a breast tumor associated with increased Notch signaling comprises administering to the subject an effective amount of an inhibitor of Notch signaling.

Abstract: A method for assaying a medium for the presence of a substance that affects an SH2-phosphorylated ligand regulatory system. The method employs an SH2-like domain or a subdomain thereof and a phosphorylated ligand. The phosphophorylated ligand is capable of interacting with the SH2-like domain or a subdomain thereof to form an SH2-phosphorylated ligand complex. The SH2-like domain or subdomain and/or the phosphorylated ligand are present in a known concentration. The SH2-like domain or a subdomain thereof and the phosphorylated ligand are incubated with a substance which is suspected of affecting an SH2-phosphorylated ligand regulatory system. The method is carried out under conditions which permit the formation of the SH2-phosphorylated ligand complex. SH2-phosphorylated ligand complex, free SH2-like domain or subdomains thereof, or non-complexed phosphorylated ligand are assayed.