Phospho-EGFR (Tyr1173) is a phosphorylated form of the epidermal growth factor receptor (EGFR), a 170 kDa transmembrane receptor tyrosine kinase that plays a crucial role in cell signaling. When EGFR binds to its ligands, such as EGF, it undergoes dimerization and autophosphorylation, activating multiple downstream signaling pathways. Phosphorylation at Tyr1173 is particularly important as it provides a docking site for proteins like the tyrosine phosphatase SHP-1, which can modulate EGFR activity and downstream signaling. This site is also involved in the MAP kinase signaling pathway, which regulates cell growth, survival, and transformation. Abnormal regulation of EGFR, including phosphorylation at Tyr1173, is often associated with various cancers, making it a key target for therapeutic interventions.