CRNN (cornulin) is a 495 amino acid protein located on chromosome 1.3 that functions primarily as a differentiation marker in squamous epithelial cells 1. CRNN promotes cell proliferation and G1/S cell cycle progression by inducing CCND1 expression and activating NFKB1 and PI3K/AKT signaling pathways 2. In normal physiology, CRNN serves as a stress response regulator with roles in keratinocyte differentiation and cell-cell adhesion. CRNN functions as a tumor suppressor in multiple squamous cell carcinomas. In esophageal squamous cell carcinoma (ESCC), CRNN expression significantly decreases during progression from precancerous lesions to invasive cancer, with reduced CRNN inhibiting cell proliferation 3. Similarly, CRNN downregulation occurs in oral 4, laryngeal 5, and cutaneous squamous cell carcinomas 6. CRNN downregulation correlates with genomic instability, microsatellite instability, and loss of heterozygosity at 1q21.3 4. CRNN overexpression suppresses tumor cell growth, migration, invasion, and promotes cell death, while CRNN knockdown reverses these effects via AKT pathway inhibition 56. CRNN downregulation is independently associated with poor prognosis and advanced staging across multiple cancer types, establishing it as a potential prognostic and therapeutic target 45.