Which histologic findings are characteristic of follicular thyroid carcinoma (FTC)?

Updated: Jun 18, 2020
  • Author: Luigi Santacroce, MD; Chief Editor: Neetu Radhakrishnan, MD  more...
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Answer

On gross examination, FTC appears encapsulated and solitary and is often found in necrotic and/or hemorrhagic areas, as depicted in the images below.

Follicular thyroid carcinoma. Surgical specimen of Follicular thyroid carcinoma. Surgical specimen of a large goiter. Total thyroidectomy was performed because of the presence of a solid nodule in the right lobe (note the size of the thyroid lobe at left of the screen).
Follicular thyroid carcinoma. The right lobe of th Follicular thyroid carcinoma. The right lobe of the thyroid was sectioned and reveals a large solid nodule with necrotic and hemorrhagic areas. Histologic diagnosis is follicular thyroid carcinoma.

Histologically, the lesion may be encapsulated and may demonstrate well-defined follicles containing colloid, making its distinction from follicular adenoma difficult. Examples of FTC are shown in the images below.

Follicular thyroid carcinoma. Histologic pattern o Follicular thyroid carcinoma. Histologic pattern of a mildly differentiated follicular thyroid carcinoma (250 X). Image courtesy of Professor Pantaleo Bufo at University of Foggia, Italy.
Follicular thyroid carcinoma. Histologic pattern o Follicular thyroid carcinoma. Histologic pattern of a rare lymph node metastasis of follicular thyroid carcinoma (140 X). Image courtesy of Professor Pantaleo Bufo at University of Foggia, Italy.
Follicular thyroid carcinoma. Histologic pattern o Follicular thyroid carcinoma. Histologic pattern of a rare lymph node metastasis of follicular thyroid carcinoma (250 X). Image courtesy of Professor Pantaleo Bufo at University of Foggia, Italy.

See the list below:

  • Histologic and cellular patterns of endocrine tumors do not allow diagnosis of carcinoma; therefore, this diagnosis is made by finding pseudocapsule and/or blood vessel invasion, not by cellular morphology.

  • High magnification of the abortive follicles may demonstrate atypia of the follicular epithelium and intervening stroma.

  • Thyrocytes are large and show an abnormal nuclear/cytoplasmic ratio with several mitoses.

  • Presence of colloid-rich follicles lined by flattened follicular cells that are occasionally accompanied by several histiocytes is maintained in a benign lesion.

  • Definitive diagnosis is often not possible with samples obtained from FNAB because accurate distinction between benign and malignant lesions cannot be made.

Because of the well-known role of the RAS-RAF-MEK-MAP kinase pathway in thyroid carcinogenesis, n-RAS expression may be evaluated to differentiate follicular and papillary cancer of the thyroid.


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