The Many Faces and Mimics of Papillary Thyroid Carcinoma

Abstract

This article provides an overview of the 15 histologic variants of papillary thyroid carcinoma listed by the 2004 World Health Organization (WHO) monograph on endocrine tumors. The histologic features, differential diagnosis, and clinical course of each variant are discussed in some detail. The follicular variants (conventional and macrofollicular) constitute a morphologic challenge because the majority of these tumors are encapsulated and, also, because, in many tumors, not all neoplastic cells show the nuclear features considered to be diagnostic of papillary carcinoma. As a result, most of these tumors are missed even by experienced pathologists. Moreover, hyperplastic thyroid lesions, follicular adenomas, and Hashimoto's thyroiditis may contain cells with clear nuclei resembling those of papillary carcinoma. Papillary carcinomas composed entirely of hyperchromatic cells have been overlooked. The WHO monograph defines papillary carcinoma with focal spindle and giant cell carcinoma components but its clinical behavior is unknown. Papillary carcinoma with an insular pattern that does not show the artifactual separation of the cell nests has been misinterpreted as the solid variant of papillary carcinoma. Papillary microcarcinomas include not only the conventional type and the follicular variants but also the tall cell and columnar cell variants.

Hobnail Variant of Papillary Thyroid Carcinoma: An Institutional Case Series and Molecular Profile

“…HVPTC has been described in other case reports and case series (12)(13)(14)(22)(23)(24)(25)(26)(27)(28)(29)(30). The architectural growth pattern for HVPTC is micropapillary (i.e., small papillae).…”

Diagnostic terminology and morphologic criteria for cytologic diagnosis of thyroid lesions: A synopsis of the National Cancer Institute Thyroid Fine‐Needle Aspiration State of the Science Conference

“…142,143 Clearly, the diagnosis of PTC should be based upon all of the above mentioned features rather than a single feature. 144,145 PTC can range in size from less than or equal to a centimeter, defined as microcarcinoma, to a large tumor mass with infiltration into surrounding neck structures.…”

Comparison of the clinicopathological behavior of the follicular variant of papillary thyroid carcinoma and classical papillary thyroid carcinoma: A systematic review and meta-analysis

“…The majority of thyroid cancer cases (~85%) are papillary thyroid carcinoma (PTC) (2). A number of PTC variants have been described, including classical, follicular, oncocytic, solid, tall cell, columnar cell, diffuse sclerosing and cribriform (3,4). Among these variants, the conventional or classical type is the most common and accounts for ≤54.2% of all PTC cases in certain reported series (5)(6)(7)(8).…”