Thyroid cancer associated with Hashimoto thyroiditis: similarities and differences in an endemic area

Background Hashimoto thyroiditis (HT) is an autoimmune lymphocytic thyroiditis and is the most common form of thyroid inflammatory diseases. The association of HT with papillary thyroid carcinoma (PTC) has been described. PTC is the most common form of malignancy associated with HT. When papillary carcinoma develops on top of Hashimoto thyroiditis, the disease tends to be less aggressive and lymph node and extra-thyroidal invasion are infrequent. Results We retrospectively examined the pathological features of our patients who were diagnosed with concomitant HT and thyroid cancer. In Egyptian patients, PTC was the main type of malignancy associated with HT (96.2%) and was often multifocal (46.2%). In contrast to the published literature, lymph node invasion and extra-thyroidal extension were as frequent in association with HT as in other cancer cohorts. We also observed the frequent occurrence of Hürthle cell metaplasia (23.1%) and the appreciable incidence of aggressive histological types of PTC (32%). Conclusion Thyroid carcinoma with HT may have some aggressive features in areas with endemic goiter background.