GRB2 (growth factor receptor-bound protein 2) is a 25 kDa cytoplasmic and nuclear adapter protein that functions as a central hub in receptor tyrosine kinase signaling 1. Its structure consists of one Src homology 2 (SH2) domain flanked by two Src homology 3 (SH3) domains, enabling it to mediate interactions between activated cell-surface receptors and downstream signaling molecules 1. GRB2 transduces signals from multiple receptor systems, including IL-5 signaling in eosinophils where it associates with Shc adapter protein to activate Ras-Raf-MAP kinase pathways 2. Beyond cytoplasmic signaling, GRB2 functions in nuclear DNA repair by stabilizing RAD51 at stalled replication forks, protecting DNA from MRE11-mediated degradation and maintaining genomic stability 3. In the endometrium, GRB2 is critical for implantation and decidualization; its reduction in endometriosis patients correlates with impaired endometrial receptivity and progesterone resistance 4. GRB2 expression is inversely regulated by miR-1271, with elevated GRB2 levels observed in endometriosis tissues 5. Clinically, GRB2 dysregulation contributes to multiple cancers through aberrant mitogenic signaling 1. Its role in replication fork protection suggests therapeutic potential; GRB2 depletion combined with PARP inhibitors enhances anti-tumor immunity in ovarian cancer models 3, positioning GRB2 as both a therapeutic target and predictive biomarker for combination immunotherapy strategies.