Differentiated Thyroid Cancer: Then and Now. A Personal Perspective

[摘要] I have spent over 40 years as a surgical pathologist in oncology. I have seen trends come and go, hype settle into reality, and continuous change happen in our conceptual understanding of cancer. I have chosen thyroid cancer to track this long journey because this field has always been in ferment. It would be impossible to write a review of all the changes in thyroid neoplasia that have occurred in my lifetime. I will therefore restrict myself to the evolution of the classification of differentiated thyroid cancer, its molecular pathology with special reference to encapsulated nodules, and the role of fine-needle aspiration cytology (FNAC) in its management. EVOLUTION OF THE CLASSIFICATION OF DIFFERENTIATED THYROID CANCER I am old enough to remember a time when thyroid cancer was classified into four types: follicular, papillary, mixed follicular and papillary, and undifferentiated. Medullary carcinoma was unrecognized until it was described by Hazard, Hawk, and Crile in 1959. Thereafter came the classification of thyroid neoplasms into those derived from follicular epithelium and those derived from C cells. PAPILLARY THYROID CARCINOMA NUCLEI AS THE DEFINING FEATURE OF PAPILLARY THYROID CARCINOMA The next major change in the classification came with the realization that mixed papillary and follicular thyroid carcinomas were essentially papillary carcinomas with follicular growth patterns. They all shared characteristic nuclear features, including the famed “Orphan Annie” nucleus [Figure 1]. These nuclei became the defining diagnostic feature of papillary thyroid carcinoma (PTC). It was soon noticed that there were tumors that were entirely follicular but exhibited the nuclear features of PTC. These were classified as follicular variants of PTC (FVPTC). Rosai in a critique wrote “… a thyroid tumor can have a papillary, follicular, solid, trabecular, or cribriform pattern of growth; it can be composed of large, small, oncocytic, clear, round, spindle, or columnar cells; it can be encapsulated, minimally invasive, or widely invasive; in sum, it can have any of those features and more, but as long as it has PTC-type nuclei it is thought to be a PTC or one of its innumerable variants.” Much of this is still the state of the art. However, with an understanding of molecular pathology in a clinical context, the PTC nuclei no longer hold the same overarching diagnostic significance as they did before.

[学科分类] 皮肤病学