Frequency and Distribution of DNA fragmentation in Hashimoto’s thyroiditis and development of papillary thyroid carcinoma

Downregulation of apoptosis and high expression of bcl-2 play an important role in the development of follicular lymphoma. However, little is known about apoptosis in thyroid disease, particularly with respect to the development of papillary carcinoma from Hashimoto’s thyroiditis. To study the early stages of cell death in various types of thyroid disease, surgical specimens from 31 patients including Hashimoto’s thyroiditis (HT,n=7), papillary carcinoma (PC,n=12), Hashimoto’s thyroiditis with papillary carcinoma (HTPC,n=5), and Graves’ disease (GD,n=7) were examined by anin situ nucleotidyl transferase assay (ISNTA), which detects DNA fragmentation. Control normal thyroid tissue (NT,n=7) was obtained from surgically resected papillary thyroid carcinomas sampled away from the primary tumor. An immunohistochemical (IHC) method was used to detect bcl-2 expression. Positive ISNTA nuclei in thyroid follicular cells or tumor cells per section were counted in all parenchymal areas, excluding areas of lymphocyte aggregates. The intensity of bcl-2 staining was graded on a scale of 1+ to 3+. The number of ISNTA-positive thyroid follicular cells was a significantly higher in HT compared to GD. In addition, there was significantly lower number of ISNTA positive non-neoplastic thyroid follicular cells in HTPC compared to HT alone. Strong expression of bcl-2 was found in all cases of GD and NT, but much less bcl-2 staining was seen in HT. There was moderate expression of bcl-2 in HTPC and PC. These findings suggest that (1) DNA fragmentation of the thyroid follicular cells plays an important role in the thyroid injury in HT but not in GD, (2) expression of bcl-2 may overcome the apoptosis in GD but not in HT, and (3) downregulation of DNA fragmentation of the follicular cells in Hashimoto’s thyroiditis associated with papillary carcinoma may suggest an important mechanism for tumor pathogenesis.