Cytokeratin subtyping in chordomas and the fetal notochord: an immunohistochemical analysis of aberrant expression.

Chordoma is a well-known bone tumor that shows epithelioid features and in which the expression of cytokeratins (CKs) has been reported to appear very frequently. Numerous immunohistochemical analyses of CK expression have been conducted using such monoclonal antibodies as CAM5.2, which react with CK8, CK18, and CK19, and AE1/AE3, which react with CKs 1-8, 10, 14-16 and 19 in chordoma. No detailed analysis, however, of the expression of each component of CK has yet been conducted in chordoma; thus, the subsets of CK expressed there have yet to be clarified. With the use of immunohistochemical techniques with a panel of monoclonal antibodies against each subset of CK, the authors studied the expression of CKs in 16 specimens of classic chordoma and 14 specimens of the fetal notochord to clarify the subsets of CK expressed in chordoma and to evaluate the similarities and differences of CK expression between chordoma and the fetal notochord. All of the chordoma specimens showed a strong positive immunoreactivity for CK8 and CK19, whereas nine (56.3%) chordoma specimens showed a positive immunoreaction for CK18. In addition, four chordoma specimens were focally positive for keratin-903, which reacts with high molecular weight CKs such as CK1, CK5, CK10, and CK14; one specimen also showed a strong CK7 expression. All of the notochord specimens were also positive for CK8 and CK19, but none showed a positive immunoreaction for keratin-903, CK7, or CK18. In addition, none of the chordoma or notochord specimens showed immunoreactivity for CK20. The expression of CK8 and CK19, observed in all of the chordoma and notochord specimens, was thus considered to be maintained throughout the neoplastic transformation, although some aberrant CK expressions (CK7, CK18, and keratin-903) also occurred in the chordoma specimens examined in this study.