GRAP2 (GRB2-related adaptor protein 2) is a leukocyte-specific adaptor protein that functions as a central linker in immune cell signaling and T-cell receptor (TCR) pathway activation 1. GRAP2 interacts with SLP-76 to regulate NF-AT activation and binds tyrosine-phosphorylated proteins including Shc, facilitating signal transduction from the plasma membrane to the nucleus 1. The protein associates with GCIP (GRAP2 cyclin-D interacting protein), which inhibits E2F1-mediated transcription and cyclin D-dependent kinase activity, thereby regulating cell proliferation and differentiation 1. GRAP2 expression is particularly relevant in cancer biology; it is significantly downregulated in lung adenocarcinoma (LUAD) and pancreatic cancer, correlating with poorer prognosis, advanced disease stage, and reduced survival 23. Mechanistically, GRAP2 downregulation positively correlates with immune infiltration in LUAD through effects on immune markers and chemokine signaling 2. Clinically, GRAP2 serves as a prognostic biomarker in lung cancer and is part of diagnostic signatures for early LUAD detection via circulating small extracellular vesicles, showing superior sensitivity to low-dose CT 4. GRAP2 expression patterns distinguish T-cell from NK-cell lineages in extranodal NK/T-cell lymphomas 5. Additionally, GRAP2-associated GCIP inhibition contributes to fibroblast-like synoviocyte overgrowth in rheumatoid arthritis 6.