Clonal relationship between Hashimoto's thyroiditis and thyroid lymphoma

Abstract

Aim: Although Hashimoto's thyroiditis (HT) is a predisposing factor for B-lineage thyroid lymphoma, clonal B-cell populations in HT are rare. We undertook this study to determine if there was a clonal relationship between HT and primary thyroid lymphoma. Methods: Clonalilty and sequence similarity was determined by polymerase chain reaction followed by sequencing and comparing Immunoglobulin heavy chain (IgH) gene rearrangement sequences to germline sequences and to each other. Results: Twelve of 20 patients with primary thyroid lymphoma had a previous history and histologic diagnosis of Hashimoto's thyroiditis. Clonal IgH bands associated with a polyclonal background were present in four of these 12 cases of HT and of these four three had reproducible clonal IgH bands from the subsequently developed lymphoma. The range of similarity (homology) of multiple clonal bands in HT with the germline IgH varied from 90% to 96.3%. Multiple clonal bands in HT had sequence similarity (homology) ranging from 62-100% with the clonal band in the lymphoma from the same patient. At least one clonal band in HT had more than 96% similarity (homology) with the clonal band of lymphoma in all three cases. Conclusion: Sequence similarity between the clonal bands in HT and subsequently developed thyroid lymphoma is supportive of the argument that primary thyroid lymphoma may evolve from HT.