Malignant T-cell lymphoma of the thyroid gland associated with Hashimoto's thyroiditis.

Reported herein is a rare case of malignant T-cell lymphoma of the thyroid gland that developed in a 71-year-old woman with a past history of chronic thyroiditis. The chief complaints were rapidly growing neck mass, weight loss and hoarseness. Presence of abnormal lymphoid cells in the peripheral blood, and an increase in anti-microsome antibodies and anti-thyroglobulin antibodies were found on preoperative laboratory tests. A diagnosis of suspicious malignant lymphoma of the thyroid gland accompanied by Hashimoto's thyroiditis was made, and a total thyroidectomy was performed. Histological examination revealed diffuse small lymphocytic infiltration in the thyroid gland associated with Hashimoto's thyroiditis. Immunohistochemical examination showed that the small lymphocytes were positive for T-cell markers with CD4 predominance. Southern blot analysis of tumor specimens revealed a monoclonal T-cell receptor gene rearrangement. Peripheral T-cell lymphoma was diagnosed. No adjuvant therapy was performed because of the tumor stage and its subtype. The patient is well with no recurrence or metastasis 25 months after the surgical removal of the thyroid. The present case suggests that Hashimoto's thyroiditis might play an important role in the carcinogenesis of thyroid lymphoma not only of B-cell lineage but also of T-cell lineage.