Hyalinizing trabecular tumor of the thyroid: an update.

Hyalinizing trabecular tumor (HTT) is a rare thyroid tumor of follicular cell origin with a trabecular pattern of growth and marked intratrabecular hyalinization. This tumor is known to share morphological and architectural similarities with paraganglioma and medullary thyroid carcinoma, as well as the nuclear features and RET/PTC1 translocations of papillary thyroid carcinoma. These tumors are not associated with RAS or BRAF mutations. Whether the presence of RET alterations in HTT are sufficient molecular proof of its relationship with papillary thyroid carcinoma (PTC) is still to be defined. Of great interest is the characteristic strong peripheral cytoplasmic and membranous staining of the tumor cells with MIB1 immunostain, not seen in any other thyroid neoplasm. Although cases of malignant HTT have been recorded, HTT should be considered a benign neoplasm or, at most, a neoplasm of extremely low malignant potential.