Chordoma is a
neoplasm of notochordal differentiation that typically occurs in the axial skeleton. Accurate diagnosis is therapeutically important but can be challenging, especially in fine-needle aspiration (FNA) and core needle biopsy (CNB). Immunohistochemistry for the
transcription factor brachyury (T) has recently proven diagnostically useful in whole-tissue sections. Our aim was to compare
brachyury performance with conventional markers (S-100, EMA,
keratin) and to evaluate its utility in distinguishing
chordoma from cytomorphologic mimics.
Brachyury immunohistochemistry was performed on
chordoma (8 FNA, 12 CNB),
chondrosarcoma (10 FNA), and metastatic
mucinous adenocarcinoma (12 FNA). Immunohistochemistry performed at the time of diagnosis was also reviewed.
Brachyury was positive in 17 (85%) cases of
chordoma and typically showed moderate-to-strong nuclear staining. Of five sets of concurrent FNA and CNB, four pairs were positive for
brachyury in both samples and one pair was positive for
brachyury in the CNB and negative in the cell block. S-100, EMA, and
keratin stains were available for 13
chordomas: 9 (69%) cases (including the 3 negative for
brachyury) were positive for S-100 and
keratin or EMA; 4 cases were
keratin positive but S-100 negative. No nuclear
brachyury staining was seen in
chondrosarcoma or
adenocarcinoma, though two
adenocarcinomas showed cytoplasmic staining.
Brachyury separates
chordoma from cytomorphologic mimics with high sensitivity and specificity in small biopsies. As a single test,
brachyury has higher sensitivity than a combined panel of S-100 and epithelial markers. When added to the conventional panel,
brachyury increases sensitivity to 100% without sacrificing specificity.