Oncocytic Variant of Medullary Thyroid Carcinoma: A Rare Case of Sporadic Multifocal and Bilateral RET Wild-Type Neoplasm with Revision of the Literature

Abstract

Oncocytic variant of medullary thyroid carcinoma (OV-MTC) is a very unusual entity, up to date only 17 cases have been reported in the literature. MTC is a neuro-endocrine malignancy arising from the para-follicular C cells of the thyroid gland. It generally has a slight female predominance and appears as a single lesion. However in the Multiple Endocrine Neoplasia Syndrome 2, linked to the point mutation of RET oncogene, multifocal MTCs may also occur. Herein, we report the case of a 75 years old man with a rare form of sporadic multifocal and bilateral OV-MTC expressing wild-type RET gene. The histological and molecular features of this rare entity are presented and discussed with revision of the pertinent literature.

Keywords: Medullary carcinoma; Oncocytic variant; RET; Thyroid.

Figure 1.

A) Different neoplastic foci, arranged in sub-centimetric nodules, scattered in the thyroid parenchyma [haematoxylin and eosin (H&E), magnification 25×]. B) Neoplastic cells show large eosinophilic and loosely granular cytoplasm. Nuclei are characterized by salt-and-pepper-textured chromatin, enhancement of nuclear membrane and occasional prominent nucleoli (H&E, magnification 100×). C) Medullary carcinoma stained for calcitonin: there is extensive infiltration of the thyroid parenchyma by tumor cells (Indirect immunoperoxidase with calcitonin specific mAB, magnification 25×). D) Sustentacular cells occur within the nodules, embracing neoplastic cells (Indirect immunoperoxidase with S-100 specific mAb, magnification 100×).