Pan CK, or Pan-Cytokeratin, is a broad-spectrum immunohistochemical marker used to detect a wide range of cytokeratins, which are structural proteins found in the epithelial cells of various tissues. This marker is employed in pathology to identify and differentiate epithelial tumors from non-epithelial neoplasms. Pan CK staining helps in diagnosing carcinomas, as it highlights epithelial cell origin, aiding in tumor classification and guiding treatment decisions. It is particularly useful in the analysis of poorly differentiated tumors, metastatic cancer, and in the evaluation of tissues where the primary tumor origin is unclear.