Thyroid neoplasms of follicular cell derivation: a simplified approach.

Thyroid tumors of follicular cell derivation are increasing in incidence. These lesions exhibit a spectrum of morphologic and behavioral features that provide the opportunity to understand malignant transformation and progression. Molecular data suggest that the thyroid undergoes a series of genetic alterations that account for the development of the various types of thyroid carcinoma. Our understanding of these tumors has progressed dramatically over the past 50 years and the classification has become complex and cumbersome. We provide a practical approach to clinical diagnosis and propose a simplified classification of these common neoplasms.