Thyroid gland
Other thyroid carcinoma
Poorly differentiated

Topic Completed: 1 November 2017

Minor changes: 16 July 2020

Copyright: 2002-2019,, Inc.

PubMed Search: (Poorly differentiated carcinoma [title]) thyroid

Related Topic: Poorly differentiated carcinoma with rhabdoid features

Shuanzeng Wei, M.D., Ph.D.
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Cite this page: Wei S. Poorly differentiated. website. Accessed August 14th, 2020.
Definition / general
Essential features
  • Intermediate grade follicular cell carcinoma with limited evidence of follicular cell differentiation
  • Insular / trabecular carcinoma
  • Primordial cell carcinoma
  • Poorly differentiated follicular carcinoma
  • Poorly differentiated papillary carcinoma
  • Solid type follicular carcinoma
  • High risk thyroid carcinoma of follicular cell origin
ICD coding
  • C73 Malignant neoplasm of thyroid gland
  • Older patients, mean age 55 - 63 years
  • 0.3 - 6.7% of thyroid carcinomas
  • More common in Europe and South America than U.S. (Mod Pathol 2010;23:1269)
  • Iodine deficiency may be a risk factor; no association with radiation exposure (Clin Oncol (R Coll Radiol) 2011;23:261)
  • Some tumors are de novo; some arise from dedifferentiation of follicular or papillary carcinoma
Clinical features
  • Large solitary thyroid mass. Patient may have a history of recent growth in a longstanding uninodular or multinodular thyroid (Am J Surg Pathol 1984;8:655)
  • Intermediate behavior between well differentiated and anaplastic carcinoma (World J Surg 2007;31:934)
  • Has nodal and hematogenous metastases and 3 year survival of 38% (Langenbecks Arch Surg 2007;392:671)
  • Extends to perithyroidal soft tissue in 60 - 70% cases
  • Vascular invasion in 60 - 90% cases
  • Regional lymph node metastasis in 15 - 65%
  • Distant metastasis in 40 - 70%
Radiology description
  • Ultrasound shows inhomogeneous hyoechoic mass (Cancer 2006;106:1286)
  • Cold on scintigraphy and positive on FDG PET
Prognostic factors
Case reports
  • Total thyroidectomy, neck dissection, radioactive iodine and suppressive thyroxine
Gross description
  • Large (median size: 5 cm), grayish white, some show soft pale areas of necrosis
  • Pushing margins, may be partially encapsulated
  • Can have satellite nodules (Am J Surg Pathol 1984;8:655)
Gross images

AFIP images:

Poorly differentiated thyroid carcinoma

Massive cervical lymph node metastasis

 Contributed by Dr. Mark R. Wick:

Various images

Images hosted on other servers:

Fig 1 - a: well demarcated tumor

Tumor with invasive growth pattern

Microscopic (histologic) description
  • Turin consensus diagnostic criteria:
    • Solid / trabecular / insular growth pattern
    • No nuclear features of papillary carcinoma
    • Presence of at least one of following: convoluted nuclei, ≥ 3 mitotic figures/10 HPF, tumor necrosis (Am J Surg Pathol 2007;31:1256)
  • Other:
      • Prototypical type insular carcinoma: solid nests (may contain microfollicules) composed of small uniform cell with round hyperchromatic nuclei or convoluted nuclei, increased mitotic figures, necrosis (Am J Surg Pathol 1984;8:655)
      • Others tumors: solid nests composed of larger more pleomorphic tumor cells; may have oncocytic cells, clear cells, signet ring cells or rhabdoid cells
      • Component of well differentiated tumor (papillary or follicular carcinoma) may also be present
      • As few as 10% of poorly differentiated carcinomas (in otherwise well differentiated carcinomas) may be associated with unfavorable prognosis (Am J Surg Pathol 2011;35:1866)
      • May have peritheliomatous pattern (tumor cells around blood vessels with necrosis of tumor cells further away from vessels), vascular and capsular invasion (Lloyd: WHO Classification of Tumours of Endocrine Organs, 4th Edition, 2017)
Microscopic (histologic) images

Contributed by Shuanzeng Wei, M.D., Ph.D.

Nests of tumor with necrosis

 Contributed by Andrey Bychkov, M.D., Ph.D.:

Follicular carcinoma with high grade progression

Case of the Month #435:

Various images

Cytology description
  • Highly cellular, crowded cell clusters with solid, trabecular or insular morphology (Cancer 2009;117:185, Cytopathology 2016;27:176)
  • Background of single cells with high N:C ratio
  • May have necrotic background and increased mitotic figures
Cytology images

Contributed by
Ayana Suzuki, Cytotechnologist, Japan

Insular pattern

Contributed by
Shuanzeng Wei, M.D., Ph.D.

Diff-Quik and Pap stains (100x)

Diff-Quik and Pap stains (400x)

Corresponding histology shows mitosis and necrosis

Images hosted on other servers:

Fig. 5: nesting pattern of cells

Fig. 1: overlapping cells with round, regular nuclei

Fig. 2: large clusters and single cells

Fig. 3: cellular nests of loosely cohesive cells

Fig. 7: overlapping cells with mild atypia

Fig. 4: small microfollicle of tumor cells

Fig. 6: vacuolated cytoplasm with round nuclei

Negative stains
Molecular / cytogenetics description
Differential diagnosis
Board review style question #1
Which of the following features are not required for the diagnosis of poorly differentiated thyroid carcinoma

  1. Absence of conventional nuclear features of papillary thyroid carcinoma
  2. Necrosis / convoluted nuclei / increased mitotic activity
  3. Solid, trabecular or insular growth
  4. Vascular invasion
Board review answer #1
D. Vascular invasion.

The Turin criteria specify solid / trabecular / insular growth, lack of conventional nuclear features of papillary thyroid carcinoma and one of the following: necrosis, convoluted nuclei or increased mitotic activity (3 or more mitoses/10 HPF). Vascular invasion may be seen in a variety of thyroid carcinomas and is an adverse prognostic factor regardless of histologic subtype or grade.
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