Types of Thyroid Cancer
Thyroid cancer is classified into three main histologic categories: differentiated thyroid carcinoma (including papillary, follicular, and Hürthle cell), medullary carcinoma, and anaplastic carcinoma, with papillary being by far the most common at 89% of cases. 1
Major Histologic Categories
1. Differentiated Thyroid Carcinoma (DTC)
Papillary Thyroid Carcinoma (PTC)
- Accounts for approximately 89% of all thyroid cancers, making it the predominant type 1
- Carries an excellent prognosis with 5-year survival rates of 98% for stages I-III 1
- 10-year survival rates reach 93-99% in the general population 2
- Arises from follicular cells of the thyroid 2
- Typically presents as a cold nodule on imaging 3
Follicular Thyroid Carcinoma (FTC)
- Represents 5.1% of thyroid cancers 1
- Has a 5-year survival rate of 90% for stages I-III 1
- 10-year survival is approximately 85% 4
- Also arises from follicular cells and presents as a cold nodule 3
Hürthle Cell Carcinoma (HCC)
- Comprises 2.2-3% of all thyroid carcinomas 1, 4
- Has a 10-year survival rate of approximately 76%, which is notably lower than papillary and follicular types 4
- Classified as a distinct subtype of differentiated thyroid cancer by the World Health Organization 4
- Defined as "pure" when Hürthle cell component exceeds 75% of the tumor 4
- Presents most commonly as a solitary cold nodule 4, 3
2. Medullary Thyroid Carcinoma (MTC)
- Accounts for 1.7-4% of thyroid cancers 1, 2
- Arises from parafollicular C-cells, not follicular epithelium 2
- Has a 10-year survival rate of 60-70% 5
- Presents as a cold nodule 3
- Associated with RET mutations and can be part of Multiple Endocrine Neoplasia type 2 (MEN2) syndrome 5
3. Anaplastic Thyroid Carcinoma (ATC)
- Represents only 0.8% of thyroid cancers but is the most aggressive type 1
- Classified as an aggressive undifferentiated tumor 1
- Has a dismal prognosis with 5-year survival rate of only 7% 1
- Most patients die within 6 months of diagnosis 6
- Presents as a cold nodule 3
Clinical Significance and Prognostic Implications
The dramatic difference in survival rates between differentiated and undifferentiated thyroid cancers underscores the critical importance of accurate histologic classification for treatment planning and prognostic counseling. 1
Key Epidemiologic Patterns
- Thyroid cancer is 2-4 times more common in women than men across all histologic types 1
- The incidence has been increasing globally, primarily due to detection of small papillary carcinomas (<1 cm) through improved imaging 1
- Despite rising incidence, mortality from thyroid cancer has declined over recent decades 1
Important Clinical Pitfalls
Common Pitfall: Treating Hürthle cell carcinoma with lobectomy alone is inadequate, as this subtype requires total thyroidectomy due to its more aggressive behavior compared to other differentiated thyroid cancers 4
Diagnostic Challenge: Molecular diagnostics are specifically not recommended for Hürthle cell neoplasms due to high false-positive rates (86% unnecessary surgery rate historically), though newer tests show improved performance 4
Critical Distinction: Medullary thyroid carcinoma arises from C-cells rather than follicular epithelium, which means it does not respond to TSH suppression therapy or radioactive iodine—treatments that are standard for differentiated thyroid cancers 2