GCSAM (germinal center-associated signaling and motility), also known as HGAL, is a B-cell adaptor protein with dual roles in lymphocyte migration and B-cell receptor signaling. Functionally, GCSAM negatively regulates lymphocyte motility by mediating IL-6-induced migration inhibition through RhoA pathway activation, which downstream activates ROCK to suppress cell movement 1. GCSAM serves as a positive regulator of BCR signaling through direct interaction with Syk kinase and the adaptor protein Grb2, facilitating BCR accumulation at membrane signaling clusters (cSMAC) 2. In disease contexts, GCSAM expression is associated with improved prognosis in primary CNS lymphoma (PCNSL), where its expression correlates with better outcomes in methotrexate-treated patients 3. Notably, GCSAM is upregulated in neuroinvasive EBV+ B-cell populations, contributing to CNS trafficking of lymphoma cells through epigenetic adaptations 4. GCSAM is also expressed in Burkitt-like lymphomas driven by EBV and Myc overexpression, where it represents a germinal center B-cell marker 5. The protein's involvement in both suppressing lymphocyte motility while promoting BCR signaling suggests a specialized role in maintaining germinal center B-cell positioning during immune responses.