Follicular thyroid carcinoma presenting as a massive chest wall tumor.

The initial presentation of follicular thyroid carcinoma is rarely related to metastatic lesions. Presented here is the case of a 70-year-old woman with the initial presentation of a 13-cm chest wall mass identified as a metastatic follicular thyroid carcinoma. The chest wall lesion had features of a poorly differentiated carcinoma with areas of necrosis, an insular growth pattern focally and increased mitotic activity. A small follicular carcinoma was subsequently identified. The primary tumor was a 1-cm well-differentiated follicular carcinoma with capsular and vascular invasion. This represents a rare presentation of a follicular thyroid carcinoma with initial recognition of a large, dedifferentiated metastatic lesion from a small primary carcinoma. Dedifferentiation and metastasis in the context of microcarcinoma is an exceptionally rare event and suggests other mechanisms may be involved in disease spread other than simply increased cell proliferation.