Papillary thyroid carcinoma is the most common type of thyroid malignancy, and CD56, a neural cell adhesion molecule, is typically down-regulated in almost all cases of papillary thyroid carcinoma. Homeobox B9 is a transcription factor, belongs to the products of the homeobox transcription factor gene family, and has been known to regulate transcription of CD56 and to promote tumorigenicity and metastasis in some malignancies. In this study, we investigated the expression and relation of homeobox B9 to reduced expression of CD56 in papillary thyroid carcinomas and also a relationship between their expression and clinicopathologic parameters. Therefore, we performed CD56 and homeobox B9 immunohistochemical staining on 72 papillary thyroid carcinomas and Western blotting on 31 papillary thyroid carcinomas. CD56 protein staining revealed that it was reduced or absent in 65 papillary thyroid carcinomas (90.3%) and was related to silencing of homeobox B9 (77.8%) (P = .003). The loss of homeobox B9 expression was associated with extrathyroidal extension (P = .002), pathologic stage of tumor (P = .01), and age older than 45 years (P = .032). However, the CD56 staining did not reveal any significant relationship with clinicopathologic features (P > .05). In conclusion, reduced expression of CD56 is associated with homeobox B9 in papillary thyroid carcinomas. Furthermore, silencing of homeobox B9 is more common in older age and is linked to extrathyroidal extension and advanced pathologic stage of papillary thyroid carcinoma.
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