Endocrine malignancies that may mimic benign lesions.

A variety of malignant tumors that occur in endocrine organs may mimic benign lesions histologically. In this article, a number of such tumors are selected for discussion, including several variants of papillary thyroid carcinoma (encapsulated follicular, diffuse sclerosing, diffuse follicular, macrofollicular, cystic, and stroma-rich), paucicellular anaplastic thyroid carcinoma, primary thyroid low grade B-cell lymphoma of mucosa-associated lymphoid tissue type, adrenocortical carcinoma, and parathyroid carcinoma. Emphasis is placed on the histological clues that are helpful for recognizing the malignant nature of these lesions.