Macrofollicular variant of papillary thyroid carcinoma.

A rare case of a macrofollicular variant of papillary thyroid carcinoma occurring in an 18-year-old male is described. The extirpated tumor, 5.5 x 5.5 x 3.5 cm in size, was well demarcated and multinodular, and histopathologically showed a predominantly macrofollicular structure reminiscent of adenomatous goiter or macrofollicular adenoma. In the tumor tissue, however, there were several small foci of microfollicular or papillary structure with the nuclei characteristic of papillary carcinoma. Parts of the macrofollicular areas also showed similar nuclear characteristics with a transition to microfollicular or papillary areas. Incomplete capsular invasion and minimal vascular invasion were also present. Additional resected specimens contained small metastatic nodules in the residual left lobe and lymph nodes. Immunohistochemistry showed a small number of p53-positive tumor cells in the microfollicular or papillary areas. It is suggested that this tumor is a well-differentiated variant which should be distinguished from benign thyroid lesions, although there have been some cases of metastases which appear related to capsular and/or vascular invasion.