Cytokeratin 7 in humans is a protein encoded by the KRT7 gene. It is always as a keratin pair with Cytokeratin 19. Cytokeratin 7 is expressed on most ductal and glandular epithelium including lung, breast, bladder and female genital tract, but not in most gastrointestinal epithelium, prostate, hepatocyte and squamous epithelium. In tumor tissues, its expression is absent in colon cancer, prostate cancer and squamous carcinomas. Cytokeratin 7 is often used in concert with Cytokeratin 20 and CDX-2 to aid in distinguishing ovarian, pulmonary and breast carcinomas (CK7+) from colon carcinomas (CK7-).