ARHGAP9 (Rho GTPase activating protein 9) functions as a GTPase activator that converts active GTP-bound Rho family GTPases to their inactive GDP-bound state, with substantial GAP activity toward CDC42 and RAC1, and lesser activity toward RHOA 1. The protein contains multiple functional domains including a Rho-GAP domain, SH3 domain, pleckstrin homology region, and WW domain 1. ARHGAP9 regulates cellular adhesion of hematopoietic cells to extracellular matrix components like fibronectin and collagen IV 1. Mechanistically, ARHGAP9 acts as a MAP kinase docking protein that inhibits ERK and p38 activation through WW domain binding, representing a novel cross-talk mechanism between Rho GTPase and MAP kinase signaling 2. The protein also regulates cancer progression through multiple pathways, including PI3K/AKT/mTOR signaling inhibition 3 and Wnt/β-catenin pathway modulation via DKK2 suppression 4. ARHGAP9 expression is predominantly found in peripheral blood leukocytes, spleen, and thymus 1. Clinical significance varies by cancer type: ARHGAP9 overexpression correlates with poor prognosis in acute myeloid leukemia 5 and clear cell renal cell carcinoma 6, while downregulation is associated with poor outcomes in hepatocellular carcinoma 7 and colorectal cancer 3.