Thyroid Oncocytic (Hu?rthle Cell) Nodules With Longitudinal Nuclear Grooves

Context.-Thyroid nodules with longitudinal nuclear grooves have been widely regarded as synonymous with papillary thyroid carcinoma (PTC).Objective.-To study a series of cases of thyroid nodules that exhibited oncocytic (Hu & BULL;rthle cell) features and contained longitudinal nuclear grooves yet failed to display aggressive behavior or the full features of papillary thyroid carcinoma.Design.-The clinicopathologic, immunohistochemical, and molecular genetic features of 15 patients with these features were studied. Next-generation sequencing was performed to examine 161 genes for oncogenic driver alterations associated with thyroid neoplasia.Results.-The lesions occurred in 11 women and 4 men aged 27 to 80 years and measured 0.2 to 2.3 cm in diameter (mean, 1.1 cm). The tumors were well circum-scribed and noninvasive and showed a proliferation of large cells with abundant granular cytoplasm and centrally placed nuclei displaying scattered longitudinal nuclear grooves. Immunohistochemical stains were negative for HBME-1, galectin-3, and CK19 in all cases. NRAS pQ61R was detected in 6 cases, KRAS p.Q61E in 1 case, and AKT2 p.E17K in 1 case. None of the genetic changes classically associated with conventional PTC or with high-grade thyroid malignant neoplasms were identified. Clinical follow-up in 9 patients showed no evidence of recurrence or metastases between 2 and 13 years (mean, 5.7 years).Conclusions.-Longitudinal nuclear grooves can be occasionally encountered in oncocytic (Hu & BULL;rthle cell) tumors and should not lead to a diagnosis of PTC in the absence of other features supporting that diagnosis.