Benign nodular goiter with spindle cell component.

We report three benign nodular goiters associated with spindle cell component. The spindle cells were bland, and showed short fascicular pattern or formed small nests. The cytoplasm was pale or clear. A transition between follicular cells and the spindle cells was observed. Immunohistochemically, they were positive for thyroglobulin and thyroid transcription factor-1. They did not react against CD34. Ki-67 (MIB-1) labeling indexes were less than 1%. We thought that the spindle cells are derived from follicular cell and non-neoplastic, and it is important to recognize this lesion to distinguish from aggressive and lethal components seen in papillary carcinoma or anaplastic carcinoma.