Most Common Thyroid Cancer Associated with Hashimoto Thyroiditis
Papillary thyroid cancer (PTC) is the most common type of thyroid cancer associated with Hashimoto thyroiditis. 1, 2
Evidence Supporting Papillary Thyroid Cancer Association
The association between Hashimoto thyroiditis (HT) and thyroid cancer has been well documented in clinical guidelines and research studies. The evidence consistently points to papillary thyroid cancer as the predominant malignancy associated with this autoimmune condition:
- A comprehensive review of 36 studies involving 64,628 subjects found a significant relative risk (RR) of HT among papillary thyroid cancer patients of 2.36 (95% CI 1.55-3.29, p < 0.001) 2
- The same study reported an RR of PTC among HT patients of 1.40 (95% CI 1.07-1.85, p = 0.016) 2
- Multiple studies confirm that PTC is the main type of malignancy associated with HT, with one study reporting it accounts for 96.2% of thyroid cancers in HT patients 3
Clinical Characteristics of PTC in Hashimoto Thyroiditis
PTC associated with Hashimoto thyroiditis typically demonstrates distinct clinical and pathological features:
- Less aggressive disease characteristics overall 1
- Superior 10-year disease-specific survival 1
- Better recurrence-free survival 1
- Decreased PTC-related mortality (HR, 0.19) 1
- Often multifocal (46.2% in one study) 3
- Higher cure rates (75.3% vs 47.1% in patients without HT) 4
- Lower rates of persistent disease (6.8% vs 22.9% in patients without HT) 4
Regional Variations and Special Considerations
It's important to note that the behavior of PTC in Hashimoto thyroiditis can vary based on geographic and endemic factors:
- In endemic goiter areas, PTC with Hashimoto thyroiditis may display more aggressive features 1, 3:
- More frequent lymph node invasion
- Higher rates of extra-thyroidal extension
- Higher incidence of aggressive histological PTC variants (32% in one study) 3
Other Thyroid Cancers Associated with Hashimoto Thyroiditis
While PTC is the most common, other thyroid malignancies can occur with HT:
- Thyroid lymphoma has a strong association with HT, with a relative risk of 9.74 (95% CI 3.93-24.13, p < 0.001) 2
- No significant association has been found between HT and follicular, medullary, or anaplastic thyroid cancer 2
Diagnostic Considerations
When evaluating thyroid nodules in patients with Hashimoto thyroiditis:
- Fine-needle aspiration (FNA) is recommended for suspicious thyroid nodules 1
- Pathology and cytopathology slides should be reviewed by a pathologist with expertise in thyroid disorders 5
- False-negative FNA results can occur, so worrisome clinical findings should not be overlooked despite reassuring FNA results 5, 1
In conclusion, papillary thyroid cancer is clearly the most common thyroid cancer associated with Hashimoto thyroiditis, followed by thyroid lymphoma, which has a less common but stronger statistical association.