Kidney tumor
Adult renal cell carcinoma
Primary thyroid-like follicular carcinoma

Author: Daniel Anderson, M.D., MBA
Editor: Maria Tretiakova, M.D., Ph.D.

Revised: 15 March 2018, last major update March 2018

Copyright: (c) 2003-2018,, Inc.

PubMed Search: Thyroid-like follicular carcinoma pathology

Cite this page: Anderson, D. Primary thyroid-like follicular carcinoma. website. Accessed March 24th, 2018.
Definition / general
  • Rare kidney tumor that morphologically mimics well differentiated thyroid follicular neoplasms
Essential features
  • Extremely uncommon (~40 cases described)
  • Resembles well differentiated thyroid follicular neoplasms
  • Encapsulated mass with prominent follicular architecture (macro and microfollicles) containing colloid or eosinophilic like material
  • Negative for TTF1 and thyroglobulin
  • Most have low malignant potential
Clinical features
Radiology images

Images hosted on other servers:

Coronal CT of mass in left kidney showing no evident enhancement between non and postcontrast

Coronal and axial CT scan of TLFCK

Case reports
Gross description
  • Solitary mass, 1 - 13 cm (mean 3.5 cm)
  • Well circumscribed and encapsulated
  • Tan to brown in color
Gross images

Images hosted on other servers:

Gross appearance of TLFCK

well defined, multiloculated cystic mass

Polycystic left kidney

Cystic light brown cut surface

Microscopic (histologic) description
  • Follicular architecture with micro and macrofollicles containing eosinophilic secretions or colloid-like material
  • Follicles may be cystically dilated (Diagn Pathol 2014;9:186)
  • May have focal tightly packed follicles without secretions
  • Follicular cells have moderate amphophilic to eosinophilic cytoplasm, round nuclei, mostly inconspicuous but occasional prominent nucleoli
  • Lymphocytic infiltrate may be present intratumoral or around periphery and macrophages may be present in background (Diagn Pathol 2013;8:108)
  • Calcifications may be seen, including abundant microcalcifications; some cases resemble atrophic thyroid tissue (Pathology 2018;50:24)
Microscopic (histologic) images

Images hosted on PathOut server:

Contributed by Maria Tretiakova, M.D., Ph.D.

Thyroid-like follicular renal cell carcinoma low and high power

Images hosted on other servers:

Colloid-like eosinophilic material

Small, compact follicles with near solid appearance

Nuclei are equivalent to Fuhrman grade 1 or 2

Variably sized follicles with colloid-like material

Desmoplastic stroma

Focus of microfollicles with near solid appearance

Follicles filled
with partially
colloid-like and
mucoid material

Invasion into the capsule

Solid area of the tumor (20x)

Various images

Cytology description
  • May be hypercellular and forming sheets (Diagn Cytopathol 2014;42:273)
  • Presence of acellular eosinophilic material is associated with the neoplastic epithelial cells in the background of the smear
  • Individual tumor cells may be oval, round and plasmacytoid with mild nuclear pleomorphism, finely stippled nuclear chromatin and inconspicuous nucleoli with moderate amount of eosinophilic cytoplasm and rare nuclear grooves (Diagn Cytopathol 2014;42:273, Diagn Pathol 2013;8:108)
Cytology images

Images hosted on other servers:


Uniform medium sized cells

Molecular / cytogenetics description
  • Gene expression profile is distinct from clear cell or chromophobe renal cell carcinoma
  • Comparative genetic hybridization failed to reveal cytogenetic alterations in one study (Am J Surg Pathol 2009;33:393)
  • Another study showed chromosomal gains of 7q36, 8q24, 12, 16, 17p11-q11, 17q24, 19q, 20q13, 21q22.3 and Xp and losses of 1p36, 3 and 9q21-33 detected by comparative genomic hybridization (Am J Surg Pathol 2006;30:411)
Differential diagnosis
  • Carcinoid tumor: rare, patterns are insular, cords, nests or ribbons but not follicular; neuroendocrine histology, positive for neuroendocrine markers synaptophysin and chromogranin
  • Metastatic follicular carcinoma arising in struma ovarii in females
  • Metastatic thyroid carcinoma: very rare to kidney, usually obvious thyroid primary with widely disseminated metastases, thyroglobulin+ or TTF1+
  • Oncocytoma: areas of classical oncocytoma with nests of oncocytic cells embedded in loose myxoid stroma
Board review question #1
The following are true about primary thyroid-like follicular carcinoma EXCEPT:

  1. Follicular architecture, often with macro and microfollicles with eosinophilic or colloid-like material
  2. Most have low malignant potential
  3. Express TTF1 and thyroglobulin
  4. PAX8 positive
Board review answer #1
C. Primary thyroid-like follicular carcinoma is a rare neoplasm with a follicular architecture often with macro and micro follicles with eosinophilic or colloid like material. The majority of these neoplasms have low malignant potential. The first major challenge is to differentiate it from metastatic thyroid carcinoma. Thyroid carcinoma should be positive for TTF1 and thyroglobulin while primary thyroid-like follicular carcinoma is usually negative. PAX8 is positive in both thyroid and renal cell carcinomas, and thus not helpful in the differential diagnosis.