Utility of immunohistochemistry in the evaluation of necrotic thyroid tumors.

We have previously shown that necrotic tumors retain their immunoreactivity for a range of cytokeratin antibodies. Some thyroid tumors undergo extensive necrosis after fine-needle aspiration (FNA) procedures. We evaluated the sensitivity of antibodies on necrotic thyroid tumors by examining a series of thyroid tumors consisting of 10 Hurthle cell neoplasms, 8 carcinomas, and 2 follicular adenomas (12 with post-FNA necrosis). These were stained with antibodies to AE1/3, PANCK, thyroglobulin and S100. Four of the cases of papillary carcinoma were also stained with antibodies to CK19. As a control for the specificity of thyroglobulin immunoreactivity in necrotic tissue, we also stained 11 nonthyroid tumors with extensive necrosis (7 carcinomas, 1 lymphoma, 2 melanomas, 1 sarcoma) for thyroglobulin. Six of 8 thyroid carcinomas were positive for AE1/3 and PANCK; AE1/3 reactivity was retained in necrotic areas of 4 of 6. AE 1/3 was positive in necrotic portions of 5 of 10 Hurthle cell lesions, whereas PANCKwas negative in all but 1. Thyroglobulin reactivity was present in 18 of 20 cases, and was preserved in necrotic portions of 5 of 6 carcinomas, as well as 8 of 10 Hurthle cell neoplasms. S100 cytoplasmic reactivity was present in 4 Hurthle cell neoplasms and 1 papillary carcinoma; this staining was lost in necrotic areas. No staining by thyroglobulin was observed in the viable or necrotic areas of nonthyroid neoplasms. The preservation of cytokeratin reactivity, measured by AE1/3, in thyroid neoplasms is a diagnostically useful feature in spontaneous and post-FNA infarction. PANCK is not a well-preserved marker in necrotic thyroid tissue. This difference may be due to detection of keratin 19 by AE1/3. Thyroglobulin is preserved in some necrotic thyroid carcinomas and in Hurthle cell lesions. Preservation of thyroglobulin reactivity in necrotic tissue is specific in that no staining was observed in nonthyroid neoplasms. These results suggest that thyroglobulin is useful in demonstrating thyroid lineage of both primary and metastatic necrotic tumor masses.