Minimally invasive thyroid anaplastic carcinoma with long survival.

Anaplastic thyroid carcinoma is a highly lethal malignancy. Previously, only five cases of a noninvasive form of anaplastic thyroid carcinoma with excellent prognosis were reported. We report a case of a 68-year-old man who presented with a 3.8 cm thyroid nodule diagnosed by fine needle aspiration biopsy as poorly differentiated spindled and epithelial malignant cells. Lobectomy and isthmusectomy were performed, and the final diagnosis was microinvasive anaplastic thyroid carcinoma arising in a poorly differentiated carcinoma. The patient remains disease-free after six years, even after hemithyroidectomy and radiation treatment. Noninvasive/microinvasive anaplastic thyroid carcinoma appears to be a different disease entity from classical anaplastic thyroid carcinoma, with favorable prognosis and long disease-free survival.