Primary localized non-Hodgkin's lymphoma of the thyroid: a retrospective clinicopathological review.

Primary localized non-Hodgkin's lymphomas (NHL) of the thyroid are rare. The data presented are derived from 819 consecutive patients with NHL and six patients with anaplastic thyroid carcinomas of small cell type investigated and treated at our department between 1970 and 1981. The present analyses are based on the 19 patients, who were found to have localized primary thyroid lymphomas. Four of these patients were initially considered to have undifferentiated small cell carcinomas of the thyroid but revealed to be lymphomas at re-examination supplemented with immunohistopathologic staining. Prognosis has been evaluated with regard to initial stage, histopathology according to the Kiel classification and therapy. Median follow-up was 5 years. The crude survival was 77% 5 years after diagnosis. This was not significantly less (4.2%) than the overall-survival in an age- and sex-matched population, despite the majority of patients having tumours which were locally advanced, often with spread to regional lymph nodes, and in many cases a histology showing a high-grade malignancy according to Kiel classification. The excellent prognosis in the current study compared to other studies is probably mainly attributed to more extensive staging procedures. The biologic behaviour supports the hypothesis that these lymphomas represent lymphomas of mucosa associated lymphoid tissue (MALT). According to present results anaplastic thyroid carcinoma of small cell type must be extremely rare.