Thyroid papillary carcinoma with solid sclerosing change in IgG4-related sclerosing disease

IgG4-related sclerosing disease (IgG4-RSD) is an inflammatory and fibrosing disorder characterized by lymphoplasmacytic inflammation with infiltration of various organs, including the pancreas, bile ducts, lung, kidney, and retroperitoneum. As for malignancy in IgG4-RSD, only limited literature is available. We report here a case of thyroid papillary carcinoma showing unique morphology in IgG4-RSD. Solid tumor nests were surrounded by dense IgG4-positive plasma cells and fibrosis at both the primary site and metastatic lymph nodes. In contrast the background thyroid showed focal lymphocytic thyroiditis. IgG4-related sclerosing sialadenitis and autoimmune pancreatitis were also diagnosed, and prednisolone treatment improved symptoms and serum IgG4 abnormality. To the best of our knowledge, this is the first documentation of a malignancy of the thyroid gland occurring in a background of IgG4-RSD. A brief review of the literature on the relationship between IgG4 and malignancy is included.