Cytokeratins 20 and 7 in the differential diagnosis of metastatic carcinoma in cytologic specimens.

A series of 33 tumor cases (13 fine-needle aspirates and 20 effusion specimens) were evaluated for the expression of two cytokeratin (CK) subtypes; CK 20, expressed primarily in tumors of the GI tract, mucinous ovarian tumors and transitional cell carcinomas, and CK 7, found chiefly in non-GI tract adenocarcinomas, including breast and lung. CK 20 expression was demonstrated immunocytochemically in seven of seven metastatic colon and two of three metastatic transitional cell carcinomas tested. CK 20 was absent in all metastatic carcinomas of breast, ovary, lung, and uterus examined (23 cases). Anti-CK 7 stains were negative in four of six metastatic colonic carcinomas, with equivocal results in the remaining two cases. Metastatic lung, breast, and ovarian carcinomas were strongly positive for CK 7. This study demonstrates that the combined use of anti-CK 20 and anti-CK 7 antibodies is highly sensitive and specific for metastatic colonic adenocarcinoma in cytologic material and thus could play an important role in distinguishing this entity from other common primary carcinomas.