The keratin 20 (KRT20) antibody is a widely used tool in diagnostic pathology and research, targeting the KRT20 protein, a member of the type I cytokeratin family. KRT20 is a 48 kDa intermediate filament protein expressed in specific epithelial tissues, including the gastrointestinal tract (particularly superficial gastric mucosa and intestinal enterocytes), urothelium (umbrella cells of the bladder), and Merkel cells of the skin. Its restricted expression pattern makes it a valuable biomarker for identifying cellular origin in tumors. In clinical practice, KRT20 immunohistochemistry (IHC) helps distinguish carcinomas of colorectal, gastric, or urothelial origin from other malignancies. For example, KRT20 positivity is common in colorectal adenocarcinoma but rare in lung or breast cancers. It is also utilized in diagnosing neuroendocrine tumors, such as Merkel cell carcinoma, where KRT20 shows a characteristic perinuclear dot-like staining. Additionally, KRT20 is often paired with KRT7 (a broadly expressed cytokeratin) to refine differential diagnoses—e.g., KRT20+/KRT7- profiles suggest lower gastrointestinal tract tumors, while KRT20-/KRT7+ may indicate pancreatobiliary or ovarian origins. Antibody validation ensures specificity for reliable results, critical for guiding treatment decisions. Research studies further explore KRT20's role in epithelial differentiation, wound healing, and disease mechanisms, such as inflammatory bowel disorders or Barrett’s esophagus. Its stability in formalin-fixed tissues enhances its utility in routine pathology workflows.