Mucosa-associated lymphoid tissue lymphoma with large cell transformation on the background of Hashimoto's thyroiditis: a case report and review literature.

Primary thyroid lymphoma (PTL) is a rare cause of malignancy that occurs in 0.5% of cases with Hashimoto's thyroiditis. The most common subtype is diffuse large B-cell lymphoma (DLBCL), followed by mucosa-associated lymphoid tissue (MALT) lymphoma. We described the case of a 70-year-old man who was diagnosed with MALT lymphoma in the background of autoimmune thyroiditis with focal area of DLBCL transformation. The patient was a 70-year-old man with rapidly growing mass of the thyroid gland with compressive symptom over two months. The laboratory data revealed primary hypothyroidism with positively anti-thyroid antibodies. The computerized tomography scan showed right thyroid mass extended to anterior mediastinum and compressed adjacent airway with multiple cervical and mediastinal lymphadenopathies. The pathology from incisional biopsy showed extranodal marginal zone B-cell lymphoma of MALT lymphoma with large cell transformation. The patient received four courses of systemic chemotherapy combined with involved field radiation therapy. The mass was dramatically decreased in size after treatment, leading to a complete resolution of compressive symptoms. Thyroid lymphoma is quite rare; however the incidence may be higher in patients with Hashimoto's thyroiditis. A rapidly growing thyroid gland should be considered as PTL. Chemotherapy and radiation are the mainstays of treatment.