Association of Hashimoto's thyroiditis and thyroid cancer

Purpose of review The association of Hashimoto's thyroiditis and thyroid cancer remains an active focus of research and controversy. Since it was first proposed in 1955, numerous studies have explored the epidemiology and etiology of these concurrent disease processes. Recent findings The lymphocytic infiltration of Hashimoto's thyroiditis is frequently encountered in thyroid glands resected for a neoplasm. The most frequent association is noted with papillary thyroid cancer. Several recent studies performed on patients undergoing thyroidectomy with coexisting Hashimoto's thyroiditis report an increased prevalence of papillary thyroid cancer, with a favorable disease profile and an improved prognosis, particularly in women. Conversely, some population-based studies using fine-needle aspiration biopsy data report no linkage between serologic Hashimoto's thyroiditis and thyroid cancer, yet they are limited by the lack of definitive pathology. On the other hand, the significantly increased incidence of primary thyroid lymphomas in patients with Hashimoto's thyroiditis strongly suggests a pathogenetic link between this autoimmune disorder and malignant thyroid lymphoma. Summary The lymphocytic infiltration of Hashimoto's thyroiditis is frequently associated with papillary thyroid cancer and may indeed be a risk factor for developing this type of cancer. Nonetheless, a pathogenesis linking these diseases remains unclear. The relationship between thyroid lymphoma and Hashimoto's thyroiditis appears to be well established.