Usefulness of S100A9 for diagnosis of intrathyroid epithelial thymoma (ITET)/carcinoma showing thymus-like differentiation (CASTLE).
OBJECTIVE
Intrathyroid epithelial tumour (ITET)/carcinoma showing thymus-like differentiation (CASTLE) is a rare malignant tumour, which is thought to originate from ectopic thymic tissue in the thyroid. The differential diagnosis between ITET/ CASTLE and squamous cell carcinoma (SCC) or undifferentiated carcinoma with squamoid component (UC-SCC) is very important, because ITET/CASTLE shows a far better prognosis than SCC or UC-SCC. In this study, we investigated the usefulness of S100A9, a marker of SCC and squamous cell epithelia, for diagnosis of ITET/CASTLE.


METHODS
We immunohistochemically investigated S100A9 expression in 23 ITET/CASTLEs, 26 SCCs, and 19 UC-SCCs, as well as eight thymomas and 12 normal thymic tissues.


RESULTS
All thymomas and thymic tissues showed a small number of S100A9-expressing cells in a scattered pattern in accordance with Hassall corpuscles. Twenty-one of 23 ITET/ CASTLEs showed the same pattern as thymomas or thymic tissues, while 14 SCCs and 15 UC-SCCs showed diffuse and laminated positivity of S100A9. The positive predictive value and specificity of S100A9 for diagnosis of ITET/CASTLE was 91.3 and 93.9%, respectively, and sensitivity was 75.0%.


CONCLUSIONS
These findings suggest that S100A9 is a useful marker for discriminating ITET/CASTLE from SCC or UC-SCC.
Ito
Yasuhiro
Y
Department of Surgery, Kuma Hospital, Kobe, Japan. ito01@kuma-h.or.jp
Miyauchi
Akira
A
Arai
Kazumori
K
Nozawa
Ryushi
R
Miya
Akihiro
A
Kobayashi
Kaoru
K
Nakamura
Yasushi
Y
Kakudo
Kennichi
K
D040502:Calgranulin B / Q000235:genetics / Q000378:metabolism*; D002294:Carcinoma, Squamous Cell / Q000175:diagnosis / Q000378:metabolism; D002454:Cell Differentiation; D003937:Diagnosis, Differential; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D009375:Neoplasms, Glandular and Epithelial / Q000175:diagnosis* / Q000378:metabolism; D011237:Predictive Value of Tests; D013945:Thymoma / Q000175:diagnosis* / Q000378:metabolism; D013950:Thymus Gland / Q000378:metabolism / Q000473:pathology; D013953:Thymus Neoplasms / Q000175:diagnosis* / Q000378:metabolism
D040502:Calgranulin B