Use

This first-line screening immunohistochemical test evaluates neoplasms of unknown origin and assists in determining epithelial cell lineage by detecting cytokeratin AE1/AE3 expression. Positive staining typically appears as filamentous cytoplasmic or membranous reactivity, suggesting epithelial origin. Note that reactivity may be variable in neuroendocrine carcinomas (e.g., small cell carcinoma), while hepatocellular carcinoma and adrenocortical neoplasms often lack reactivity. CK AE1/AE3 does not detect CK9, CK12, CK17, or CK18, and cross-reactivity can occur in select non‑epithelial cells such as glioblastoma. Interpretation should be performed in the clinical and pathological context by a qualified pathologist.