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.