Mucoepidermoid Carcinoma of the Thyroid with Concomitant Papillary Carcinoma: Comparison of Findings on Fine-Needle Aspiration Biopsy and Histology

Abstract

We report two cases of mucoepidermoid carcinoma (MEC) of the thyroid gland coexisting with, and possibly arising in, papillary thyroid carcinoma (PTC). In the first case, CT-guided fine-needle aspiration (FNA) was performed on a paratracheal mass representing extrathyroidal invasion of a right thyroid lobe tumor. The aspirate showed papillary fronds and cells in honeycombed arrangements with fine chromatin, enlarged nuclei, nuclear grooves, and intranuclear inclusions in a background of mucus and blood; a diagnosis of PTC was rendered initially. However, examination of histologic sections of the mass showed nests of malignant squamous cells with interspersed mucous cells and extracellular mucin, concordant with MEC, as well as PTC. A retrospective review of the FNA specimen identified MEC. In the second case, ultrasound-guided FNA was performed on a right thyroid lobe nodule. The aspirate contained two populations of epithelial cells: larger cells showing foci of both squamous and glandular differentiation that were interpreted as MEC and smaller follicular cells with nuclear changes characteristic of PTC; both were addressed in the diagnostic report. Primary MEC of the thyroid is a rare neoplasm typically exhibiting indolent clinical behavior, although our first case demonstrated extensive local invasion. It is thought to arise from squamous metaplasia associated with PTC, Hashimoto thyroiditis, or other inflammatory or neoplastic processes. In thyroid FNAs, the presence of neoplastic mucous cells and extracellular mucin plus malignant squamous cells is diagnostic of MEC. As MEC is thought to arise in PTC, the finding of the latter in these aspiration specimens is not unexpected.

Composite Mucoepidermoid Carcinoma and Columnar Cell Variant of Papillary Carcinoma of the Thyroid

“…Prognosis seems to be good, and disease-free survival exceeding 10 years have been observed. 10,14 However, in many cases reported in the literature, the patients presented with locally advanced tumors at diagnosis, [4][5][6]8,10,11,[16][17][18] in the form of local invasion or of cervical lymph node metastasis, as in our patient. Local recurrence can also occur.…”

“…The most frequently found is PCT, which was associated with MEC in 13 of the cases reported in the literature. [3][4][5][6][7][8][9][10][11][12][13][14] The other histological types reported in association with MEC are follicular carcinoma, 7 Hurtle cell carcinoma, 7 poorly differentiated carcinoma, 6 and anaplastic carcinoma. 11,15 We report the first case of mixed MEC and PCT variant, classified as predominantly columnar cell variant.…”

Composite poorly differentiated mucoepidermoid carcinoma of the thyroid and follicular variant of papillary thyroid carcinoma. Report of a case and review of the literature

“…In cases with only locoregional spread, treatment with total thyroidectomy, neck dissection and external radiation, has been shown to give good clinical outcomes [6]. But direct invasion into neck viscera has been shown to be a poor prognostic factor and in such cases treatment with surgery and radiotherapy have been unsuccessful in halting advancement of the disease [6, 8, 9]. Early histopathological diagnosis prior to spread by direct invasion is therefore advantageous in prognosis and treatment options [6, 8].…”

Pitfalls in Challenging Thyroid Tumors: Emphasis on Differential Diagnosis and Ancillary Biomarkers

“…8d and e ). In about half of these neoplasms, an association with PTC (conventional, follicular, columnar cell, or tall cell variants) has been reported [ 2 , 95 , 96 ]. In some cases (with or without PTC), poorly differentiated and/or anaplastic carcinoma component may be seen, and such cases have been linked to a worse prognosis [ 97 ].…”