Hashimoto’s thyroiditis (HT) is the most common autoimmune disease which causes hypothyroidism. The pathogenesis of HT is based on an abnormal humoral and cellular immune response against thyroid autoantigens which cause chronic inflammation at thyroid gland. Histologically, HT is characterized by diffuse lymphocytic infiltration (DLI) with numerous lymphoid follicles, fibrosis and parenchymal atrophy.
Because chronic inflammation may be strongly associated with various human cancers, it has long been postulated that HT would be associated with an increased risk of thyroid cancer. Indeed, it has been noticed for a long time that DLI is frequently associated with papillary thyroid cancer (PTC). Many retrospective studies also reported that co-occurrence of HT in PTCs is associated with a better outcome with lower recurrence rates. However, the role of HT in the development and progression of PTC is still debated. The observed effect may be partly due to the modulation of the tumor microenvironment, the induction of immune responses, and also the presence of positive prognostic factors such as female sex, younger age, smaller tumors, lack of extrathyroidal extension, lymph node or distant metastases, earlier TNM stage and low frequency of BRAF mutations in PTCs with HT.
In this session, I’ll review recent studies evaluated the association between HT and the development and prognosis of thyroid cancer, especially PTC, and discuss many hypothesis regarding their association.