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thyroid solid cell nests

Thursday 29 March 2012

Definition: Solid cell nests (SCNs) are remnants of the ultimobranchial body that have been found in 61% of human thyroid glands serially sectioned.

Microscopy

Thyroid “solid cell nest” are small basaloid cell clusters corresponding to ultimo-branchial remnants, which may contain microcysts, without cytological atypia.

SCNs are composed of solid (squamoid) and/or cystic structures of main cells (negative for thyroid transcription factor-1 [TTF-1], thyroglobulin, and calcitonin) admixed with rare C cells.

Sometimes, mixed follicles lined by main cells and follicular epithelium, as well as microcysts, papillae, and ciliated cells, can be associated with SCNs.

Immunohistochemistry

Rare C-cells (chromogranin A positive); no or weak staining for thyroglobulin (TG) and TTF1; strong expression of p63 protein.

Physiopathology

Although their biologic meaning is unknown, it has been proposed that the main cells of SCNs harbor some properties of a stem cell phenotype such as the capacity for self renewal, conferred by telomerase activity, and for differentiation to one or more types of specialized cells, given the high expression of p63 and bcl-2.

According to the cancer stem cell hypothesis, a histogenetic relationship between SCNs and some thyroid carcinomas has been widely debated in the literature.

SCN hyperplasia

SCN hyperplasia has been reported as single giant SCNs or as multiple small nests.

Associations

Continuity between SCN lesions and papillary thyroid carcinoma also sharing BRAF or RAS mutations has been reported.

More recently, a primary small cell (basaloid) carcinoma of the thyroid displaying SCN features has also been reported.

Variants

- oncocytic thyroid solid cell nests (SCNs)

  • SCNs with oncocytic (Hürthle cell) features

References

- Absence of the BRAF and the GRIM-19 Mutations in Oncocytic (Hürthle Cell) Solid Cell Nests of the Thyroid, Am J Clin Pathol, 2012