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Thyroid cancer

Last updated: March 31, 2020


The majority of thyroid cancers are well-differentiated carcinomas. The principal risk factors are exposure to ionizing radiation and genetic predisposition; thyroid cancers also disproportionately affect women. A distinction is made between well-differentiated thyroid carcinomas (papillary or follicular carcinoma) and poorly differentiated carcinomas (medullary or anaplastic carcinoma); the two groups vary considerably with regard to treatment options, metastatic pathways, and prognosis. Papillary thyroid carcinomas are the most common type of thyroid cancer. Early detection is crucial for improving the prognosis but challenging because symptoms often appear late in the course of the disease. Imaging plays a central role in detection: nodules that appear hypoechoic on ultrasound and cold on scintigraphy should raise suspicion of malignancy. Additional testing is needed to determine the type of thyroid cancer, including measuring hormone levels, tumor markers, and/or biopsy via fine-needle aspiration. Most thyroid cancers are treated surgically (hemithyroidectomy or thyroidectomy), followed by thyroid hormone therapy to replace physiological hormone production and to limit the growth stimulus for any remaining metastases. Further therapeutic measures depend on the type of thyroid cancer involved and include radioiodine therapy and possibly chemotherapy.



Epidemiological data refers to the US, unless otherwise specified.



Overview of the most common types of thyroid cancer

Tissue of origin Carcinoma Differentiation Characteristics Distribution Peak incidence
Thyrocytes Papillary thyroid carcinoma


  • ∼ 80% of cases
  • 30–50 years of age

Follicular thyroid carcinoma

  • ∼ 10% of cases
  • 40–60 years of age

Anaplastic thyroid carcinoma


  • ∼ 1–2% of cases
  • After 60 years of age
Parafollicular cells (C cells)

Medullary carcinoma

  • < 10%of cases
  • 50–60 years of age

Remember that Papillary carcinoma is the most Prevalent type of thyroid cancer, that it features Palpable lymph nodes, and that it has the best Prognosis compared to all other types of thyroid cancer.


Subtypes and variants


Clinical features

Only 25% of thyroid carcinomas detected on ultrasound had previously manifested with clinical signs or symptoms!



Laboratory tests


Ultrasound [10][11][12]

  • Hypoechoic thyroid lesions with irregular margins > 1 cm are potentially malignant although normal echogenicity does not rule out carcinoma!
  • Malignancies often show microcalcifications; (typical for papillary thyroid carcinomas)

Thyroid scintigraphy

  • Indications:
  • Findings: decreased tracer uptake suggests a malignant non-functioning (cold) nodule.

Nodules that appear hypoechoic on ultrasound and cold in scintigraphy are highly suspicious for malignancy!

Fine-needle aspiration (FNA)




Papillary carcinoma

Psammoma bodies [18]

“Orphan Annie” eyes nuclei

Nuclear grooves [19]

To memorize that papillary thyroid cancer is histologically characterized by psammoma bodies and Orphan Annie-eye nuclei, imagine that “Papi and Moma adopted Orphan Annie.”

Follicular carcinoma [20]

  • Uniform follicles
  • Vascular and/or capsular invasion

Medullary carcinoma [21]

  • Ovoid cells of C cell origin and therefore without follicle development
  • Amyloid in the stroma (stains with Congo red)

Remember that medullary carcinoma is composed of C-cells producing Calcitonin and is characterized by amyloid aCCumulation staining with Congo red.

Anaplastic thyroid carcinoma [22]


References: [24]

Differential diagnoses


The differential diagnoses listed here are not exhaustive.


Well-differentiated cancers

Poorly-differentiated cancers


  • Accidental removal of parathyroid glands → hypocalcemia [25]
  • Transection of superior and recurrent laryngeal nerve → dysphonia (hoarseness), dysphagia
    • May occur during ligation of the superior laryngeal artery and inferior thyroid artery due to the proximity of the nerves to the arteries.
    • If only the external branch of the superior laryngeal nerve is damaged, complete loss of voice is unlikely, but a loss of vocal range may occur (with potentially career-damaging consequences for occupational voice users, e.g., singers).





Thyroid cancer

5-year survival rate


> 90%









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