Cytokeratin 7 (CK7) labeling can aid in differentiating between lung,1 breast, and urothelial cancers, which are typically positive, and colon and prostate cancers, which are often devoid of CK7 expression.2-7 CK7 is a frequent marker for primary lung adenocarcinomas and is also seen in other primary lung carcinomas and non-pulmonary carcinomas.1 Furthermore, anti-cytokeratin 7 has proven helpful in the differential diagnosis of ovarian malignancies.8 Anti-cytokeratin 7 interacts with proteins that are present in the majority of epithelial cells in the biliary duct, ductal, glandular, and transitional tissues.