“Noninvasive Follicular Thyroid Neoplasm With Papillary-Like Nuclear Features” With Focal Spindle Cell Metaplasia

Abstract

"Noninvasive follicular thyroid neoplasm with papillary-like nuclear features" (NIFTP) is a recent reclassification of the encapsulated follicular variant of papillary thyroid carcinoma, which is supposed to reflect its indolent clinical behavior and to prevent overtreatment of patients with this neoplasm. The diagnosis of NIFTP can only be made histologically on the surgical specimen according to specific inclusion and exclusion criteria, which requires the examination of the whole nodule and its capsule. Spindle cell proliferations, especially of follicular cell origin, arising within thyroid follicular neoplasms are very rare and may cause diagnostic difficulties. Few reports described spindle cell proliferations arising in follicular thyroid adenoma and papillary thyroid carcinoma. To the best of our knowledge, only one case has been reported in NIFTP so far. In this article, we report a unique case of NIFTP associated with a spindle cell proliferation that was characterized immunohistochemically. Specific issues related to this case are discussed.

Spindle cell variant of follicular thyroid carcinoma: An extremely unusual case and review of the literature

“…Spindle cell proliferations, especially of follicular cell origin and arising within thyroid follicular neoplasms are rare. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] In the largest published series, Vergilio et al described spindle cell proliferations in 10 patients arising in association with PTC (N = 7, including three follicular variants) and FTA (N = 3). 21 These measured 0.3-3.0 cm, constituted from 1% to 95% of the tumor, and were either admixed with the neoplastic elements or located at the periphery of the primary tumor.…”

“…Spindle cell proliferations, especially of follicular cell origin and arising within thyroid follicular neoplasms are rare 7–24 . In the largest published series, Vergilio et al described spindle cell proliferations in 10 patients arising in association with PTC ( N = 7, including three follicular variants) and FTA ( N = 3) 21 .…”

“…2,7 Spindle cell proliferations arising within well-differentiated thyroid follicular neoplasms are the least common. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] These are usually focal but rarely, the spindle cell component can predominate and potentially obscure the usual component of the neoplasm, posing diagnostic difficulties. Only few cases of the spindle cell variant of follicular thyroid carcinoma (ScV-FTC) have been reported.…”

“…Rarely, ectopic thymus cells or solid cell nests can develop into intrathyroidal thymic tumors including thymoma, thymic carcinoma, and spindle epithelial tumors with thymus‐like differentiation (SETTLE) 2,7 . Spindle cell proliferations arising within well‐differentiated thyroid follicular neoplasms are the least common 8–21 . These are usually focal but rarely, the spindle cell component can predominate and potentially obscure the usual component of the neoplasm, posing diagnostic difficulties.…”