Poorly Differentiated Thyroid Carcinoma: The Turin Proposal for the Use of Uniform Diagnostic Criteria and an Algorithmic Diagnostic Approach

TLDR

Poorly differentiated thyroid carcinomas occupy an intermediate position between well‑differentiated and anaplastic types, yet inconsistent diagnostic criteria have caused widespread confusion among clinicians and pathologists. The study aimed to compare geographic variations in PD carcinoma lesions and to establish consensus diagnostic criteria through an international panel of thyroid pathologists. Eighty‑three cases from Europe, Japan, and the United States were anonymously reviewed by 12 pathologists, followed by a blind diagnosis and the development of an algorithmic approach for practical use. Consensus criteria were defined as a solid/trabecular/insular growth pattern lacking papillary nuclear features, combined with at least one of convoluted nuclei, ≥3 mitoses per 10 high‑power fields, or tumor necrosis.

Abstract

Poorly differentiated (PD) thyroid carcinomas lie both morphologically and behaviorally between well-differentiated and undifferentiated (anaplastic) carcinomas. Following the original description of this entity, different diagnostic criteria have been employed, resulting in wide discrepancies and confusion among pathologists and clinicians worldwide. To compare lesions occurring in different geographic areas and the diagnostic criteria applied in those countries, we designed a study with a panel of internationally recognized thyroid pathologists to develop consensus diagnostic criteria for PD carcinomas. Eighty-three cases were collected from Europe, Japan, and the United States, and circulated among 12 thyroid pathologists. Diagnoses were made without any knowledge of the clinical parameters, which were subsequently used for survival analysis. A consensus meeting was then held in Turin, Italy, where an agreement was reached concerning the diagnostic criteria for PD carcinoma. These include (1) presence of a solid/trabecular/insular pattern of growth, (2) absence of the conventional nuclear features of papillary carcinoma, and (3) presence of at least one of the following features: convoluted nuclei; mitotic activity ≥3×10 HPF; and tumor necrosis. An algorithmic approach was devised for practical use in the diagnosis of this tumor.