Part of “CHAPTER 46 – THYROIDITIS“

Perineoplastic thyroiditis is a term used to describe thyroiditis in a gland containing a thyroid neoplasm. Most commonly, this refers to lymphocytic thyroiditis in the tissue surrounding a thyroid neoplasm, most often a papillary thyroid carcinoma (PTC), but this finding has also been reported in medullary thyroid cancer. The frequency with which perineoplastic lymphocytic infiltration in PTC occurs varies with race and sex. It has been suggested that the lymphocytic thyroiditis represents an autoimmune reaction to the thyroid neoplasm and that it may be beneficial in reducing the spread of the tumor. Lymphocytes derived from tissue containing PTC are unusual, because they express both CD4 and CD8 markers and may display intense cytolytic activity in vitro. Significantly improved outcomes occur in PTC and medullary thyroid cancer patients who have lymphocytic infiltration when compared with patients with these tumors and no lymphocytic tissue response.73 This finding may, if confirmed, be useful in treatment planning for patients with thyroid cancer.74 Despite the increased incidence of thyroid lymphoma in patients with Hashimoto thyroiditis, clinical lymphocytic thyroiditis generally is not regarded as a significant premalignant lesion and was found in only ˜1% of PTC cases in one series.73 Therefore, the removal of thyroid glands containing chronic lymphocytic thyroiditis, which might be aimed at preventing the development of a thyroid neoplasm, does not seem justified. The coexistence of thyroiditis and a neoplasm in the same gland indicates that caution must be exercised in the interpretation of a thyroid biopsy that demonstrates thyroiditis. Because the lymphocytic changes are often noted near or mixed with the tumor, a biopsy of a tumor may show only thyroiditis. Multiple biopsy samples should allow sampling of actual tumor tissue and prevent the cancer from being missed.