Hyalinizing trabecular tumors of the thyroid gland are almost all benign.

In 1987, Carney et al reported 11 thyroid tumors with the following features: circumscription or encapsulation, trabecular architecture with intratrabecular hyalin and colloid, polygonal and spindle cells, nuclei with frequent grooves and cytoplasmic inclusions, occasional psammoma bodies, and a low mitotic rate. The neoplasms did not recur or metastasize during a follow-up period that averaged 10 years, and they were titled hyalinizing trabecular adenomas. Subsequently, the nuclear features of the neoplasm led to the introduction of 2 modified titles for it, hyalinizing trabecular tumor and hyalinizing trabecular neoplasm. Later, discovery of RET/PTC mutations in the tumor resulted in it being designated as a type of papillary thyroid carcinoma. We studied 119 neoplasms of the type outlined, collected over a 20-year period, for invasion, recurrence and metastasis, and obtained follow-up in 96% of the cases. One hundred eighteen tumors showed no evidence of aggressive behavior (capsular, vascular, and parenchymal invasion), local recurrence, or metastasis. One tumor showed vascular and capsular invasion, and pulmonary metastasis. We conclude that the overwhelming majority of hyalinizing trabecular tumors of the thyroid behave as benign neoplasms and that, at this time, hyalinizing trabecular adenoma is the most appropriate title for them.