Immunohistochemical and molecular pathologic subclassification of thyroid tumor with prominent hyalinizing trabecular pattern

Abstract

The purpose of this study was to evaluate the immunohistochemical and molecular pathologic characteristics of thyroid tumors with a prominent hyalinizing trabecular pattern (TTHTP). The immunohistochemical stains for TTF-1, thyroglobulin, CD56, cytokeratin (CK) 19, galectin-3, and Ki-67 were performed on 16 cases of TTHTP, and genetic analysis for BRAFV600E point mutation were studied on 12 of 16 cases. All TTHTPs were positive for TTF-1 and thyroglobulin, and nine cases expressed CD56 and Ki-67. Out of these nine cases, seven satisfied the strict criteria of Carney, and four cases were positive for CK19 or/and galectin-3 and negative for Ki-67 and CD56. The remaining three cases had no Ki-67, CD56, CK19 or galectin-3 expression. BRAFV600E mutation was detected in only one of 12 cases, showing immunohistochemical characteristics of PTC type. Eleven of 12 cases lacked BRAFV600E mutation.All TTHTPs meeting the criteria of Carney were hyalinizing trabecular tumors (HTT), and TTHTPs which did not satisfy the criteria of Carney were subclassified according to the immunohistochemical results into HTT type [Ki-67 (+) and CD56 (+)], PTC type [CK19 or galectin-3 (+)/Ki-67 (-) and CD56 (-)], or null type [Ki-67 (-), CD56 (-), CK19 (-) and galectin-3 (-)]. TTHTPs with typical histological features or with typical immunohistochemical manifestations can be categorized as HTT, and the remaining TTHTPs should be categorized as PTC or null type. Moreover, the absence of BRAFV600E mutation of TTHTP is valuable for the diagnosis of HTT.