Macrofollicular variant of papillary thyroid carcinoma with minor insular component.

Background: The macrofollicular variant of papillary thyroid carcinoma that is the subject of this study has only recently been characterized. Information about its morphologic spectrum and biologic behavior is limited.

Methods: The authors reviewed 29 examples, including 17 previously reported cases. The clinical and pathologic features of five patients who had the macrofollicular variant of papillary thyroid carcinoma with a minor insular component were analyzed in detail. The insular component in thyroid carcinomas has been associated with aggressive clinical behavior.

Results: The ages of the 5 patients ranged from 31 to 70 years; the mean age was 40 years. Three patients presented with a palpable thyroid nodule and two with a large thyroid mass of long duration. The latter two tumors, which metastasized, were the largest (8 and 11 cm) and showed extrathyroidal and blood vessel invasion. All five tumors were composed predominantly of macrofollicles (>50%) and had a minor insular component that comprised less than 5% of the tumor mass. In most tumors, the macrofollicles were lined by cells with large, clear, grooved nuclei, and all five contained areas of conventional follicular variant of papillary thyroid carcinoma. In the two that metastasized, however, the lining of many macrofollicles consisted of cuboidal cells with small, hyperchromatic, follicular-type nuclei. Only the macrofollicular component was identified in the metastatic deposits in these two patients. All five patients were alive at last follow-up, two with metastases; but follow-up for this study is limited.

Conclusions: A minor insular component is an additional feature of the macrofollicular variant of papillary thyroid carcinoma that may aid in diagnosis and does not appear to have an adverse effect on the excellent prognosis of patients with these tumors.