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Trisomy 17 as a Marker for a Subset of Noninvasive Thyroid Nodules with Focal Features of Papillary Carcinoma: Cytogenetic and Molecular Analysis of 62 Cases and Correlation with Histological Findings

Dipartimento di Scienze e Tecnologie Biomediche (D.V.F., P.Ca., T.D., R.V.) and Citomorfologia (M.L.L., P.Co., G.F.), University of Cagliari, 09042 Monserrato (CA), Italy; and Dipartimento Clinico di Scienze Radiologiche e Istocitopatologiche (L.M., G.T.), University of Bologna, 40127 Bologna, Italy

Address all correspondence and requests for reprints to: Roberta Vanni, Dipartimento di Scienze e Tecnologie Biomediche, Università di Cagliari, Cittadella Universitaria, 09042 Monserrato (CA), Italy. E-mail: vanni{at}unica.it.

Context: Differentiated carcinomas of the thyroid are divided into follicular thyroid carcinoma and papillary thyroid carcinoma (PTC), based on their propensity to invade and their cytological features [papillary carcinoma-type nuclear changes (PTC-NCs)]. PTC typically exhibits a diploid karyotype sometimes with inv10(q11.2q21.2), leading to rearranged RET gene. Follicular thyroid carcinomas are often aneuploid and may exhibit t(2;3)(q13;p25), resulting in PAX8-PPAR1 gene fusion. Isolated trisomy 17 has rarely been reported in thyroid lesions, and its significance is unknown.

Objective/Design: Our objective was to determine whether isolated trisomy 17 corresponds to a specific histological or molecular thyroid tumor subset. Nine cases with isolated trisomy 17 were critically reviewed and investigated for RAS and BRAF mutations and for RET and PAX8-PPAR1 rearrangements.

Results: All nine cases were noninvasive, exhibited follicular growth pattern, and showed PTC-NCs focally defined within the nodule: four were PTCs follicular variant within larger tumors, and five were follicular-patterned nodules with incomplete cytological features of papillary carcinoma (variable proportion of cells with PTC-NCs scattered inside the lesion). RAS, BRAF^V600E mutation, RET or PAX8-PPAR1 rearrangements were not identified. One case had BRAF^K601E mutation. Only two of the 53 control cases showed focal PTC-NCs.

Conclusions: Isolated trisomy 17 is associated with focal papillary carcinoma changes in follicular-patterned thyroid nodules and may be a marker for this subset of thyroid lesions that are often difficult to classify.

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