Table 1.

Morphology and molecular findings in overlapping thyroid lesions

Thyroid tumor	Morphology	IHC	Genetic alterations
HTT	Nests and cords of cells showing oval-spindle nuclei with nuclear pseudoinclusions and abundant intratrabecular hyaline material	KI67/ MIB-1 [cell membrane positivity] Thyroglobulin	PAX8/GLIS1 PAX8/GLIS3 Wild type BRAF and RAS
PTC	Papillary and follicular structures with nuclei having irregular border, grooves and pseudoinclusions	HBME-1, Galectin-3 and CK19	BRAF V600E mutation
NIFTP	Encapsulated tumor made of follicular structures (with no papillae) and more or less prominent nuclear irregularities and pseudoinclusions (as for PTC)	Thyroglobulin and PAX8	RAS mutations THADA fusion PAX8/PPARγ BRAF K601E mutation [Wild type BRAF V600E]
MTC	Spindle or plasmacytoid cells with round oval eccentric nuclei containing salt and pepper chromatin in a more or less abundant amorphous stroma (amyloid-rich)	Calcitonin CEA	Different alterations according to sporadic or familial MTC involving RET gene
Paraganglioma	Circumscribed tumor with nesting (zell ballen) or trabecular architecture made of roundish or spindle cells with minimal atypia	Neuroendocrine markers and S100	SDHA (or B or C or D) germline mutations
FA	Encapsulated tumor made of follicular structures with round homogeneous nuclei	Thyroglobulin	RAS mutation

HTT hyalinizing trabecular tumor, PTC papillary thyroid carcinoma, NIFTP non-invasive follicular thyroid neoplasm with papillary-like nuclear features, MTC medullary thyroid carcinoma, FA follicular adenoma, IHC immunohistochemistry