Hyalinizing trabecular tumor (HTT) of the thyroid is a neoplasm of follicular derivation with a histogenesis that is still the subject of debate. Morphologic affinities between HTT and papillary carcinoma, including nuclear pseudoinclusions and grooves, suggest that these tumors may be of similar origin. The authors investigated the relationship between these two types of tumors by assessing HTT for the presence of rearrangements of the proto-oncogene rearranged during transfection (RET) that, in thyroid tumors, are specific for papillary carcinoma. A series of 14 HTTs, including two cases associated with classic papillary carcinoma, was studied by means of immunohistochemistry and reverse transcription–polymerase chain reaction. Seven follicular adenomas with focal hyalinized trabecular areas served as control cases. Three of the 14 HTT cases under consideration displayed rearrangements of RET generating the RET/papillary thyroid carcinoma type 1 (PTC1) oncogene. In another case, RET expression was detected focally by immunohistochemistry alone. Finally, in one mixed HTT–papillary carcinoma sample, RET/PTC1 expression was detected, but only in the papillary component. None of the control follicular adenomas contained rearrangements of RET/PTC. These findings demonstrate that a comparable percentage (28.6%) of HTTs and papillary carcinomas exhibit the same RET proto-oncogene alterations. Thus, HTT may represent the “hyalinizing trabecular” variant of papillary carcinoma rather than a separate entity.
From the Dipartimenti di Anatomia Patologica, Università di Torino (M.P., M.V., G.B.) e di Padova (A.Fa.); the Istituto Nazionale dei Tumori di Napoli (A.G., G.C.), Fondazione Senatore Pascale, Naples; the Centro di Endocrinologia ed Oncologia Sperimentale del CNR c/o Dipartimento di Biologia e Patologia Cellulare e Molecolare (M.S.), Università di Napoli “Federico II”; and the Dipartimento di Medicina Sperimentale e Clinica (A.Fu.), Università di Catanzaro, Italy.
Supported in part by grants from the Italian Ministry of University & Research, Rome (60% to M.P.); and the Italian Association for Cancer Research (AIRC), Milan (M.S., G.B.), Italy.
Address correspondence and reprint requests to Mauro Papotti, MD, Department of Pathology, University of Turin, Via Santena 7, I-10126 Torino, Italy; e-mail: firstname.lastname@example.org