NPAS2 (neuronal PAS domain protein 2) is a transcriptional activator that forms a core component of the circadian clock, functioning as a heterodimer with BMAL1 to regulate ~24-hour rhythms in gene expression 1. It binds DNA at E-box sequences and activates transcription of clock genes and clock-controlled genes involved in metabolism, sleep, and other physiological processes 1. NPAS2 plays critical roles in circadian regulation of metabolic pathways, DNA damage response, and neuroinflammation; for instance, the astrocyte circadian clock regulates inflammatory gene expression through NPAS2-dependent mechanisms 2. Clinically, NPAS2 dysfunction is associated with multiple cancers. High NPAS2 expression correlates with poor prognosis in gastric cancer, with elevated expression linked to advanced TNM stage, metastasis, and shortened overall survival 3. In lung adenocarcinoma, NPAS2 dampens chemosensitivity by enhancing DNA damage repair through H2AX mRNA stabilization 4. NPAS2 genetic variants influence cancer patient outcomes; for example, a GGC repeat polymorphism associates with melanoma susceptibility 5, and SNP rs2305158 predicts overall survival in non-small-cell lung cancer, particularly modulating the effect of lymph node metastasis 6. These findings suggest NPAS2 expression and variants may serve as prognostic biomarkers and therapeutic targets in cancer management.