Chronic thyroiditis as a risk factor of B-cell lymphoma in the thyroid gland

In order to contribute to the etiological study of thyroid lymphomas, the development of lymphomas in pre-existing chronic thyroiditis was statistically investigated. A total of 5592 female patients (older than 25 years) with chronic thyroiditis diagnosed between 1965 and 1982 at Kuma Hospital in Hyogo Prefecture were followed up until December 31, 1984. From a total of 45623 person-years, 8 new cases of primary thyroid lymphoma were observed (O), all of which were judged to be B-cell type from their immunological or histopathological characteristics. Since the expected number of cases with malignant lymphomas (E1) and the expected number of cases with thyroid lymphomas (E2) were 2.45 and 0.10, respectively, the O/E1 and O/E2 ratios were 3.3 (P less than 0.01) and 80.0 (P less than 0.001), respectively. The average follow-up interval for the patients with thyroid lymphoma was 9.2 years. In the reference group, consisting of cases with Basedow's disease, an increased risk of thyroid lymphoma was not observed. The present results suggest that autoimmune reactions with a notable lymphocytic infiltrate may play an important role in the etiology of lymphomas in the thyroid gland.