Histopathofogy, zyxwvutsrqponml 1990. zyxwvutsrqpon 17, 201 -209 Primary lymphoma of the thyroid: a clinical, histological and immunohistochemical study of 20 cases zyx Y.MIZUKAM1, T.MICHIGISHIt, A.NONOMURA, S.NAKAMURA*, T.HASHIMOTOS, S.KATSUDA§, S.OTAKE*, & F.MATSUBARA zyxw Pathology Section and Departments of * lnternal Medicine, t Nuclear Medicine and $ . Laboratory Medicine, Kanazawa University Hospital and 9 Department of Pathology, Kanazawa University School of Medicine, Kanazawa, Japan Date of submission 25 August 1989 Accepted for publication 4 April 1 9 9 0 MIZUKAMI Y.. MICHIGISHI T.. NONOMIJHA A , , NAKAMUHA zyxwvut S.. HASHIMOTO T., KATSUDA S., OTAKE S. & MATSUBARA F. (1990) Histopathology 17, 201-209 Primary lymphoma of the thyroid: a clinical, histological and immunohistochemical study of 20 cases Twenty cases of malignant lymphoma arising in the thyroid gland were studied clinically, histologically and immunohistochemically. Nineteen cases were non-Hodgkin's lymphoma (1 zyxwvuts 5 diffuse and four follicular lymphoma) and one was a plasmacytoma. Immuno- histochemical analysis of the lymphomas using paraffin-embedded sections disclosed that 1 7 lympho- mas were B-cell type and two were T-cell type. The Keywords: thyroid. lymphoma, immunohistochemistry plasmacytoma was of IgG kappa type. The large majority of the lymphomas were associated with an underlying chronic thyroiditis. The 5-year survival rate of the patients was 70%. An unfavourable diagnosis was more likely when the tumour was diffuse rather than follicu- lar, when it was of diffuse large cell type or of immuno- blastic type and when there was cervical lymph node involvement. Introduction Malignant lymphomas arising in the thyroid gland are relatively uncommon'-Xand their histological diagnosis has sometimes been difficult because of the lack of microscopic criteria for diagnosis. In the past, cases of high-grade lymphoma were referred to as small or large cell anaplastic thyroid carcinoma ''.'''. However, recent developments in immunohistochemical procedures have made this distinction easy, using antibodies to epithelial membrane antigens (EMA), to cytokeratin or to leucocyte common antigens (LCA) in formalin-fixed, paraffin-embedded material. The immunoperoxidase method is also satisfactory for the demonstration of intracellular immunoglobulins in B-cell lymphomas or the cell surface antigens of T-cells or B-cells. In addition, the current histopathological classifications for malig- nant lymphomas, such as the Working Formulation" Address for correspondence: Ilr Y.Mizukami. Pathology Section. Kanazawa University Hospital. 1 3- 1 , Takara-machi. Kanazawa. 920, Japan. and Kiel classificationI2. have been applied to these tumours and can be useful in more accurately predicting the prognosis. The aims of the present study were as follows: to review the histological features of a retrospective series of malignant lymphomas involving the thyroid and to reclassify them using the Working Formulation. to evaluate the histological prognostic factors and, finally, to determine the T- and B-subsets of the lymphomas with a view to improving our understanding of their histo- genesis. Materials and methods The cases were selected retrospectively from the patho- logy files of the Kanazawa University Hospital (Kana- xawa) and the Fukui Hospital (Fukui). A total of 20 cases (1 9 non-Hodgkin's lymphoma and one plasmacytoma) during the 2 5-year period 1964-1 988 was available for study (1 7 from the Kanazawa [Jniversity Hospital and three from the Fukui Hospital). In 16 cases a thyroidec- 201