STN1 is a core component of the CTC1-STN1-TEN1 (CST) complex, a single-stranded DNA-binding protein essential for telomere maintenance and genome stability 1. As part of the CST complex, STN1 binds telomeric DNA with high affinity and works with DNA polymerase α/primase to perform fill-in synthesis at the 5' ends of chr10, complementing telomerase's 3' end extension 12. Beyond telomeres, STN1 protects stalled replication forks from aberrant nucleolytic degradation through phosphorylation-dependent mechanisms involving CaMKK2 and ATR-CHK1 kinases 3. The CST complex also regulates DNA double-strand break repair pathway choice by suppressing DNA end resection, thereby favoring non-homologous end joining over homologous recombination 4. Notably, STN1 exhibits context-dependent functions independent of its CST complex role: it promotes pancreatic cancer metastasis by activating EMT transcription factor ZEB1 through R-loop-mediated STAT3 recruitment 5, and facilitates proper DSB repair and cell cycle checkpoint maintenance in KRAS-driven pancreatic cancer 6. Mutations in STN1 cause Coats plus, a telomere biology disorder characterized by pathological telomere shortening 2, and STN1 expression is tightly regulated by upstream overlapping reading frames that reduce protein levels 7.