CEACAM4 is a granulocyte-expressed cell adhesion molecule belonging to the carcinoembryonic antigen-related (CEACAM) family that functions as a phagocytic receptor. This orphan receptor contains an immunoreceptor tyrosine-based activation motif (ITAM) in its cytoplasmic domain that is phosphorylated by Src family protein tyrosine kinases upon receptor clustering, enabling efficient phagocytosis of bacteria and attached particles 1. The ITAM recruits SH2 domain-containing proteins including Src PTKs, PI3K, and the adapter molecule Nck, with deletion or inhibition of this pathway blocking phagocytic function 1. CEACAM4 shows restricted tissue distribution, being specifically expressed in medullary thyroid carcinoma cells among tumor types examined, with two novel splice variants identified in these cells 2. Unlike other CEACAM family members, CEACAM4 is not a receptor for Neisserial Opa proteins 3. In renal cell carcinoma, CEACAM4 emerged as a hub gene associated with sunitinib resistance and immune infiltration patterns 4. Additionally, CEACAM4 serves as a component of the SeptiCyte™ LAB gene expression assay, an FDA-cleared test for distinguishing infectious from non-infectious causes of systemic inflammation in critically ill patients 5. The protein's role in tumor immunotherapy represents an emerging clinical application within the broader CEACAM family 6.