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Kenneth D. Burman, Is Poorly Differentiated Thyroid Cancer Poorly Characterized?, The Journal of Clinical Endocrinology & Metabolism, Volume 99, Issue 4, 1 April 2014, Pages 1167–1169, https://doi.org/10.1210/jc.2014-1549
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Poorly differentiated thyroid cancer (PDTC) has remained a controversial diagnosis. Some clinicians refer to PDTC as thyroid cancers that do not trap radioiodine on radioiodine scans (either initially or during monitoring), and others believe that it is appropriate to refer to rapidly growing thyroid cancers that have apparently not responded to radioactive iodine therapy (1). However, in many instances it is difficult to determine whether radioiodine therapy has been partially effective. We and others had noted that “poorly differentiated thyroid carcinoma is a concept proposed to include carcinomas of follicular thyroid epithelium that retain sufficient differentiation to produce scattered small follicular structures and some thyroglobulin, but generally lack the usual morphologic characteristics of papillary and follicular carcinoma” (2–4).
In separate reports, Sakamoto et al (3) in 1983 and Carcangiu et al (5) in 1984 initially pathologically described the discrete category of PDTC. However, these authors used different characteristics to define this entity, resulting in a long-standing dispute regarding the appropriate pathological definition of PDTC. The World Health Organization tumor classification attempted to better define this entity, but this also has been considered controversial (6, 7). In an effort to quell the controversy, a group of established pathologists and investigators set forth what is referred to as the Turin proposal. This proposal set forth specific histological characteristics to attempt to universally define PDTC (7). These criteria include: 1) the presence of a solid/trabecular/insular pattern of growth; 2) the absence of the conventional nuclear features of papillary carcinoma; and 3) the presence of at least one of the following features: convoluted nuclei, mitotic activity ≥ 3 per 10 high-power fields, and tumor necrosis (7). However, PDTC remains a clinically and pathologically inchoate disorder, and it is not known whether it represents a single clinical or molecular entity. Furthermore, the optimal clinical approach for monitoring and treatment modalities is unknown.
