Pitfalls in the 2017 TNM Classification of Thyroid Carcinoma

The objective of this article is to detail the 2017 tumor-node-metastasis (TNM) staging criteria for thyroid cancer. The literature presents only few contributions, with controversial results, about comparison between previous and the new TNM systems. The 2017 TNM classification categorizes either thyroid carcinomas only limited to the gland either carcinomas macroscopically infiltrating into defined anatomical structures. The “minimal extrathyroid spread” into the perithyroidal adipose tissue no longer appears as a classification parameter in the new TNM. In the present paper is discussed for the pT categories pT1a, pT1b, pT2, and pT3a. In detail, the T-categories pT1a, pT1b, pT2, and pT3a are each subdivided into true thyroid-restricted carcinomas (pT1a1, pT1b1, pT2a1, and pT3a1) and “minimal extrathyroid proliferation” carcinomas (pT1a2, pT1b2, pT2b, and pT3a2). As a basis, a strict definition of the “minimal extrathyroid propagation” of thyroid carcinomas is essential. Although the suggestion made with the additional substrate characterization makes the work of the pathologist more intricate in daily use, standardized fundamentals for demonstrating or excluding the prognostic and therapeutic relevance concerning a “minimal extrathyroid extension” in thyroid carcinoma appear to be necessary