Is Hashimoto's (Hashimoto's thyroiditis) a risk factor for thyroid cancer?

From the Guidelines

Hashimoto's thyroiditis is not explicitly mentioned as a risk factor for thyroid cancer in the provided evidence, but based on the most recent and highest quality studies, it is generally considered that autoimmune thyroiditis, such as Hashimoto's, may be associated with an increased risk of thyroid cancer, particularly papillary thyroid carcinoma. The incidence of thyroid cancer has been increasing over the years, with a significant proportion of cases being micropapillary thyroid carcinomas, which have an excellent long-term prognosis 1. When evaluating thyroid nodules for potential malignancy, fine needle aspiration cytology (FNAC) is a crucial diagnostic tool, especially for nodules larger than 1 cm or those with suspicious clinical or ultrasonographic features 1. Key points to consider in the diagnosis and management of thyroid cancer include:

• Thyroid cancer presents as a thyroid nodule, which can be detected by palpation or neck ultrasound
• FNAC should be performed on any thyroid nodule >1 cm or those <1 cm with suspicious features
• Thyroid function tests and thyroglobulin measurement have limited utility in diagnosing thyroid cancer, but serum calcitonin measurement can be helpful in diagnosing medullary thyroid cancer
• Initial treatment for differentiated thyroid carcinoma typically involves total or near-total thyroidectomy, with or without central node dissection, depending on the presence of nodal disease. Given the potential link between Hashimoto's thyroiditis and thyroid cancer, patients with Hashimoto's should undergo regular monitoring, including periodic thyroid examinations and appropriate imaging when indicated, to promptly evaluate any new or growing thyroid nodules.

From the Research

Hashimoto's Thyroiditis and Thyroid Cancer Risk

• The relationship between Hashimoto's thyroiditis and thyroid cancer is complex, with some studies suggesting an association between the two conditions 2, 3, 4, 5.
• A prospective study found that the risk of thyroid carcinoma in patients with thyroid nodules associated with Hashimoto's thyroiditis was not significantly different from those without Hashimoto's thyroiditis (1.0% vs 2.7%, p = 0.19) 6.
• However, other studies have reported an increased prevalence of thyroid cancer in patients with Hashimoto's thyroiditis, with one study finding a prevalence of 45.7% in patients with Hashimoto's thyroiditis compared to 29% in those without 3.
• The presence of Hashimoto's thyroiditis may also increase the risk of developing papillary thyroid carcinoma, with one study finding that Hashimoto's thyroiditis was an independent risk factor for this type of cancer 5.
• The relationship between Hashimoto's thyroiditis and thyroid cancer may be influenced by factors such as thyroid function and the presence of thyroid autoantibodies, with some studies suggesting that high levels of thyroid peroxidase antibodies may protect against the development of thyroid cancer 4.

Ultrasonographic and Histopathologic Characteristics

• The ultrasonographic characteristics of malignant nodules in patients with Hashimoto's thyroiditis are similar to those in patients without Hashimoto's thyroiditis 6, 3.
• The histopathologic characteristics of papillary thyroid carcinoma in patients with Hashimoto's thyroiditis are also similar to those in patients without Hashimoto's thyroiditis 3.
• However, the presence of Hashimoto's thyroiditis may affect the detection of thyroid cancer, with one study finding that bilateral thyroid microcarcinoma was more often detected in patients with Hashimoto's thyroiditis 5.

Clinical Implications

• The association between Hashimoto's thyroiditis and thyroid cancer has implications for the clinical management of patients with Hashimoto's thyroiditis, with some studies suggesting that these patients may require closer monitoring for the development of thyroid cancer 2, 5.
• The relationship between Hashimoto's thyroiditis and thyroid cancer is complex and requires further study to fully understand the underlying mechanisms and clinical implications 2, 3, 4, 5.