MCM3 (minichromosome maintenance complex component 3) is a core component of the MCM2-7 replicative helicase complex essential for eukaryotic DNA replication. As part of the CDC45-MCM-GINS (CMG) helicase, MCM3 unwinds template DNA during replication fork elongation and contributes differentially to helicase activity through its ATPase site interactions with neighboring subunits 1. The protein is required for S phase entry and cell division. Beyond its canonical replication function, MCM3 serves as a physical barrier restricting cohesin-mediated loop extrusion during G1 phase, with potential roles in determining sister chr6 cohesion sites 2. In cancer contexts, MCM3 expression is elevated and functionally oncogenic. In esophageal squamous cell carcinoma, the FTO/LINK-A/MCM3/HIF-1α axis promotes cell proliferation and chemoresistance through MCM3 phosphorylation and altered HIF-1α interactions 3. In hepatocellular carcinoma, MCM3 overexpression correlates with microvascular invasion, advanced stage, and reduced survival, driving epithelial-mesenchymal transition via the AKT/Twist signaling pathway 4. MCM3 was identified as a hub gene in osteosarcoma metastasis networks 5. These findings establish MCM3 as both a fundamental replication factor and an emerging oncogenic driver with therapeutic potential.