Mucin-producing signet ring cell adenoma of the thyroid

Primary Benign and Malignant Thyroid Neoplasms With Signet Ring Cells: Cytologic, Histologic, and Molecular Features

OBJECTIVES

Signet ring cells (SRCs) can be seen in a variety of thyroid tumors and can pose a diagnostic pitfall on cytology. This study describes the cytologic, histomorphologic, and molecular aspects of a cohort of primary thyroid tumors with SRCs.

METHODS

A search was performed of the Massachusetts General Hospital and Brigham and Women's Hospital (Boston, MA) pathology archives for the keywords thyroid, signet, and signet ring features between 2000 and 2014. Seven thyroidectomy specimens with corresponding thyroid fine-needle aspiration (FNA) were obtained. Cytology and histopathology slides were evaluated. Molecular analysis was performed using anchored multiplex polymerase chain reaction (AMP).

RESULTS

The cohort consisted of four follicular adenomas (FAs), two noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTPs), and one secretory carcinoma (SC). The FNA diagnoses were atypia of undetermined significance (n = 3), suspicious for follicular neoplasm (n = 3), and suspicious for malignancy (n = 1). Molecular analyses revealed PTEN and FGFR3 mutations in an FA and NIFTP, respectively, and an ETV6-NTRK3 fusion in a case of primary thyroid gland SC.

CONCLUSIONS

Our study demonstrates the range of thyroid tumors with SRCs. While most thyroid tumors with SRCs are benign, primary thyroid SC should also be considered in the differential diagnosis.

Solid cell nests of the thyroid gland: morphological, immunohistochemical and genetic features

AIMS

The correct identification of solid cell nests (SCNs) is an important issue in thyroid pathology because of the spectrum of differential diagnoses of this type of lesion.

METHODS AND RESULTS

Ten cases of 295 consecutive thyroidectomies showed the presence of SCNs at histological examination. The identification of the exact SCN type required the distinction of the cystic and solid pattern; SCNs were usually composed of a mixture of main cells (MCs) and C-cells (CCs). The immunohistochemical calcitonin stain identified CCs easily, both inside SCNs and dispersed in islets at the periphery. For the characterization of MCs, we added the utility of p40 to p63. The use of thyroid transcription factor-1 (TTF-1) helped in their identification, as MCs did not react with this marker; the combination of TTF-1 and p40 or p63 IHC stains was useful for the characterization of cystic SCNs of both types 3 and 4. The negativity of mouse monoclonal mesothelioma antibody (HMBE-1) and a very low proliferative index (MIB-1) supported the diagnosis. [Correction added on 23 November 2015, after online publication: MIB-1 was incorrectly defined, the expanded form was deleted.] We discourage the use of galectin-3 (Gal-3) and cytokeratin-19 (CK-19), as they have an important overlap with papillary thyroid carcinoma. The complete absence of any B-Raf proto-oncogene, serine/threonine kinase (BRAF) mutations is an additional fundamental finding.

CONCLUSIONS

We reviewed the most relevant morphological and immunohistochemical features of SCNs and have provided a genetic analysis of the BRAF gene because of its expanding use in thyroid pathology.

Follicular adenoma with extensive extracellular mucin deposition: report on two cases

We report two cases of follicular adenoma of the thyroid with extensive extracellular mucin deposition. Fine needle aspiration in Case 1 showed singly discohesive polygonal cells in a granular mucinous background. They contained abundant eosinophilic cytoplasm, nuclear irregularities, and frequent nuclear inclusions with occasional bizarre mitoses. A right lobectomy was done. In Case 2, a 47-year-old Caucasian woman with multinodular goiter had total thyroidectomy and a yellow-tan nodule was found within the right lobe. Both tumors were well-encapsulated masses with thick capsules. Each was characterized by microfollicles without papillae in a mucinous stroma. Tumor cells were positive for thyroglobulin and negative for calcitonin, CEA, galectin-3, HBME-1, and CK19. The extracellular mucin stained with Alcian-blue and colloidal iron but not with mucicarmine and D-PAS. No BRAF gene mutation was detected. Because there were neither capsular nor vascular invasions, both cases were diagnosed as follicular adenomas of the thyroid with extensive extracellular mucin deposition, which as proposed by the WHO classification can be categorized as a mucinous variant of follicular adenoma. Retrospectively, frequent nuclear inclusions and the absence of nuclear grooves in the mucin-containing background of cytologic smears and histologic sections were shared by those of mucin-producing papillary carcinoma. It is unclear whether it belongs to an existing category of thyroid neoplasm with mucin production or whether it is truly a new tumor variant. Furthermore, pathologists should pay attention to avoid misdiagnosis of this variant of follicular neoplasm that shows an overlapping cytology with that of papillary carcinoma.