Combined tall cell carcinoma and Hürthle cell carcinoma (collision tumor) of the thyroid.

Tall cell carcinoma and Hürthle cell carcinoma are 2 aggressive forms of differentiated follicular-derived thyroid carcinomas. We present a case where these malignant tumors of thyroid coexisted. The tumor originated in the thyroid as a mixed tumor and metastasized as a tall cell tumor to the lymph nodes and as a Hürthle cell carcinoma to lungs. The coexistence of these tumor types is rare and sheds light on the histogenesis of Hürthle cell tumors and the metastatic behavior of combined tumors.