Oncocytic Follicular Cell–Derived Thyroid Tumors With Papillary Growth Pattern: A Clinicopathologic Study of 32 Cases

* Context.--Oncocytic thyroid tumors displaying a papillary growth pattern are rare and may cause diagnostic problems. Objective.--To examine the clinicopathologic features of a series of 32 follicular cell-derived tumors composed of cells with oncocytic cytoplasm and displaying papillary architecture. Design.--Thirty-two cases were collected and studied to assess clinicopathologic features, including immunohistochemical and molecular testing for BRAF V600E. Results.--The patients were 26 women and 6 men, aged 17 to 77 years. The nodules ranged from 0.3 to 6.0 cm. Eighteen cases showed features of oncocytic hyperplastic nodules and were identified against a background of thyroid follicular nodular disease; 4 cases showed features of oncocytic follicular adenoma; and 10 cases corresponded to carcinomas with oncocytic and papillary features. Nuclear features of papillary thyroid carcinoma were absent or exceedingly rare. All cases were negative for HBME-1 and cytokeratin 19 (CK19) and wild type for BRAF V600E. Follow-up in 25 patients showed that all patients with hyperplastic nodules and oncocytic follicular adenomas were alive and well and free of disease from 7 to 20 years. One patient with oncocytic follicular carcinoma showed metastases and died of tumor at 16 months; 2 patients with carcinoma had metastases and recurrence at 6 and 7 years; and 5 patients with invasive tumors were free of disease from 5 to 10 years. Conclusions.--Oncocytic thyroid tumors with papillary features can span a spectrum from benign hyperplastic, to encapsulated neoplastic, to invasive malignant lesions. Owing to their papillary features, it is important not to confuse them for other types of thyroid tumors, such as oncocytic papillary thyroid carcinoma. (Arch Pathol Lab Med. 2024;148:997-1006; doi: 10.5858/arpa.2023-0309-OA)