RAB5A is a small GTPase that serves as a key regulator of early endocytic trafficking and membrane vesicle fusion 1. The protein functions by cycling between inactive GDP-bound and active GTP-bound states, with the GTP-bound form recruiting downstream effectors responsible for vesicle formation, movement, and fusion 1. RAB5A mediates the fusion of plasma membranes with early endosomes and is essential for receptor internalization, including EGFR and C5a receptor trafficking 21. The protein facilitates EEA1 recruitment to early endosomes and coordinates with β-arrestin2 in G protein-coupled receptor signaling pathways 1. In cancer contexts, RAB5A promotes tumor cell fluidity and active wetting behaviors that facilitate invasion 3. The protein also regulates extracellular vesicle production through endosomal trafficking mechanisms, maintaining GTP-bound activation states that sustain EV biogenesis 4. Additionally, RAB5A modulates cellular senescence and autophagy pathways, with reduced expression associated with mitochondrial dysfunction and impaired differentiation in aging skeletal muscle 5. Clinically, RAB5A expression correlates with pancreatic cancer prognosis and bone marrow niche remodeling in acute myeloid leukemia, highlighting its potential as a therapeutic target 67.