Sub-section: Thyroid Section: Endocrine

Definition

Incidence

Same as papillary
Iodine deficiency is a major risk factor
Can be part of familial neoplastic syndromes such as Cowden syndrome, Carney complex.

Mutations in RAS oncogene found in 40% of patients (higher than papillary thyroid caner).
Not associated with BRAF mutations

Painless thyroid mass, usually solitary
Co-exists with multi-nodular goitre in 10%
Hoarse voice and fixed on exam concerning
- Suggest advanced disease and poor prognosis
- Need to look for tracheal extension and distant mets with CT/MRI neck and chest
Typically haematogenous spread (10-15%)
- Common sites lytic bone lesions or lung
Lymphatic spread in <10% of cases

Malignancy of thyroid epithelial cells with wide spectrum of microscopic changes
- Can range from virtually normal follicular architecture and function, to severely altered architecture
Diagnosis cannot be made on FNA/cytology
Diagnosis relies on demonstrating follicular cells in abnormal positions
- Capsular invasion
- Vascular invasion
Cells may not demonstrate nuclear atypia
- Present on diagnosis = Worse prognosis
If no invasion or nuclear atypia seen
- Follicular adenoma, not carcinoma

Now known as - Oncocytic carcinoma of the thyroid
- Was considered to be a variant of follicular thyroid cancer. However, recent clinical and molecular studies clearly indicate that oncocytic carcinoma of the thyroid is a distinct tumor type
Encapsulated tumour containing more than 75% oncocytic cells
- Large cell with abundant eosinophilic cytoplasm due to the accumulation of mitochondria
  - Characteristic appearance due to increased mitochondria (in response to cell stress)
  - Enlarged, granular eosinophilic cytoplasm
Occurs in older patients (60-75 yrs)
Higher likelihood of local recurrence
Less avid so less likely to absorb RAI
More aggressive biologic behaviour
Associated with LN mets in 30% of patients (c.f <5% of regular FTCs)