What is the relationship between papillary thyroid carcinoma and Hashimoto's (Hashimoto's thyroiditis)?

From the Guidelines

Patients with Hashimoto's thyroiditis have an increased risk of developing papillary thyroid carcinoma and should be closely monitored with regular thyroid ultrasounds and fine-needle aspiration biopsies of suspicious nodules. The relationship between papillary thyroid carcinoma and Hashimoto's thyroiditis is complex, and the chronic inflammation associated with Hashimoto's may make the diagnosis of papillary carcinoma more challenging, as lymphocytic infiltration can mask malignant changes 1. Therefore, a high index of suspicion and thorough evaluation of thyroid nodules is crucial in these patients.

Key Considerations

• Regular monitoring with thyroid ultrasounds and fine-needle aspiration biopsies is essential for early detection of papillary thyroid carcinoma in patients with Hashimoto's thyroiditis.
• The autoimmune background of Hashimoto's thyroiditis may influence the prognosis of papillary thyroid carcinoma, with some studies suggesting a better outcome for papillary carcinomas arising in this setting 1.
• Active surveillance may be considered as a management strategy for low-risk papillary microcarcinoma, but this approach requires careful monitoring and regular follow-up to detect any signs of progression 1.

Management Approach

• If papillary carcinoma is diagnosed in a patient with Hashimoto's, the standard treatment is total thyroidectomy followed by radioactive iodine ablation, typically with 30-100 mCi of I-131.
• After surgery, patients should be started on thyroid hormone replacement therapy, usually with levothyroxine at a dose of 1.6-1.8 mcg/kg/day.
• TSH should be suppressed to <0.1 mIU/L initially, then maintained between 0.1-0.5 mIU/L long-term to reduce the risk of recurrence.
• Follow-up should include regular neck ultrasounds, thyroglobulin measurements, and whole-body scans as needed.

From the Research

Relationship Between Papillary Thyroid Carcinoma and Hashimoto's Thyroiditis

• The coexistence of papillary thyroid carcinoma (PTC) and Hashimoto's thyroiditis (HT) has been observed in several studies, with a significant proportion of PTC patients also having HT 2, 3, 4, 5, 6.
• Research suggests that the presence of HT may have a protective effect on the characteristics and outcomes of PTC, with some studies finding smaller tumor sizes, reduced angioinvasion, and decreased extrathyroidal extension in HT patients 2, 3, 6.
• However, other studies have found no significant difference in the clinicopathological characteristics of PTC between HT and non-HT patients 2, 5.
• The management and follow-up of PTC in HT patients is generally no different from that of PTC alone, but providers should be vigilant about the coexistence of these phenomena and consider total thyroidectomy for cases with a cytologic diagnosis of HT with PTC 3, 4.
• The prognosis of PTC concurrent with HT is often better compared to age and stage-matched PTC, with lower recurrence and disease-free survival rates 3, 6.

Clinicopathological Characteristics

• Studies have found that PTC associated with HT tends to have a smaller mean diameter, lower frequency of extra-thyroid extension, and earlier clinicopathological staging 2, 3, 6.
• Lymph node metastases were found to be reduced in several studies, while others found no difference or increased central lymph node metastases in HT patients 2, 3.
• Multifocality is more common in PTC patients with HT, which may impact outcomes and treatment decisions 2, 4.

Association and Correlation

• A correlation between the presence of PTC and HT has been recognized, with a significant proportion of HT patients also having PTC 4, 5.
• The association between HT and PTC may indicate that HT is a precursor of thyroid cancer, but further studies are required to confirm this hypothesis 5.