Mucin-producing oncocytic thyroid carcinoma-A rare report with literature review.

The presence of mucin is a rare feature in thyroid lesions. It has been documented in a few cases of follicular neoplasms, medullary carcinoma, papillary carcinoma, poorly differentiated carcinoma, mucoepidermoid carcinoma of the thyroid, and metastasis. A 65-year-old woman presented with complaints of anterior neck swelling. The cytological features were Bethesda category III. The right thyroidectomy showed an oncocytic tumor along with luminal and intracytoplasmic mucin. Alcian blue with periodic acid Schiff stain highlighted the acidic nature of the mucin. It was an encapsulated angioinvasive tumor. On immunohistochemistry, tumor cells were positive for thyroglobulin. We report the fourth case of mucin-producing oncocytic thyroid carcinoma with its associated uncommon features, like dominant intracellular mucin, and encapsulated angioinvasion, with a literature review. Since there are only a few case reports on this topic, future studies are warranted to understand its histogenesis, tumor biology, and progression.