RET/PTC activation in hyalinizing trabecular tumors of the thyroid

Hyalinizing trabecular tumor (HTT) of the thyroid is a neoplasm of follicul ar derivation with a histogenesis that is still the subject of debate. Morp hologic affinities between HTT and papillary carcinoma, including nuclear p seudoinclusions and grooves, suggest that these tumors may be of similar or igin. The authors investigated the relationship between these two types of turners by assessing HTT for the presence of rearrangements of the proto-on cogene rearranged during transfection (RET) that, in thyroid tumors, are sp ecific for papillary carcinoma. A series of 14 HTTs, including two cases as sociated with classic papillary carcinoma, was studied by means of immunohi stochemistry and reverse transcription-polymerase chain reaction. Seven fol licular adenomas with focal hyalinized trabecular areas served as cont! ol cases. Three of the 14 HTT cases under consideration displayed rearrangemen ts of RET generating the RET/papillary thyroid carcinoma type 1 (PTC1) onco gene. In another case, RET expression was detected focally by immunohistoch emistry alone. Finally, in one mixed HTT-papillary carcinoma sample, RET/PT C1 expression was detected, but only in the papillary component. None of th e control follicular adenomass contained rearrangements of RET/PTC. These f indings demonstrate that a comparable percentage (28.6%) of HTTs and papill ary carcinomas exhibit the same RET proto-oncogene alterations. Thus, HTT m ay represent the "hyalinizing trabecular" variant of papillary carcinoma ra ther than a separate entity.