Thyroid carcinoma with mixed tall-cell and columnar-cell features. Tall-cell and columnar-cell carcinomas have been regarded as aggressive variants of papillary thyroid carcinoma. In the present case report the authors describe a composite tumor where these forms of differentiation coexisted, with transitional changes occurring within single follicular structures. This finding indicates that the two variants are closely related. In local recurrences, one or the other feature appeared in separate lesions. Lung metastases developed, and the patient died 5 1/2 years after diagnosis and primary treatment. 