Crucial parameters in thyroid carcinoma reporting - challenges, controversies and clinical implications

Abstract

In the modern era, a pathology report of thyroid carcinoma requires the inclusion of numerous prognostically relevant histopathological features, e.g. the presence and extent of vascular and capsular invasion, extrathyroidal extension, the surgical margin status and the characteristics of nodal metastasis. These pathological features are crucial components of the initial risk stratification to determine the need for completion thyroidectomy and/or postoperative radioactive iodine ablation therapy. The current review aims to summarise the diagnostic criteria, the controversies, the prognostic impacts and the challenges of these pathological characteristics, focusing specifically on the parameters that are incorporated into the American Joint Committee on Cancer (AJCC) staging system, the College of American Pathologists (CAP) reporting template, the American Thyroid Association (ATA) and the National Comprehensive Cancer Network (NCCN) guidelines.

Keywords: AJCC staging; extrathyroidal extension; lymphovascular invasion.

Figure 1

Extrathyroidal extension (ETE). (A/B) Gross ETE: A patient with papillary thyroid carcinoma (PTC) with pre-operative radiological evidence of invasion into trachea. Macroscopically (A), an infiltrative firm beige mass was present involving thyroid gland proper and infiltrating between tracheal rings (T). Microscopically, the carcinoma infiltrated in between tracheal cartilage and was present at the tracheal mucosal surface. This tumor should be staged as pT4a based on gross ETE into trachea. (C/D) Microscopic (minimal) ETE: tumor nests were present in between perithyroidal adipose tissue (FAT, panel C) or skeletal muscle (M, panel D).

Figure 2

Adverse outcome (defined as the presence of disease at last follow-up) according to degree of extra-thyroid extension (ETE) in papillary thyroid carcinoma cases with adequate follow-up. Only patients with gross ETE (15 cases) had an adverse outcome. There was no survival difference between patients without ETE (11 cases) and those with microscopic (micro) ETE (31 cases). Reprinted with permission from reference .

Figure 3

Microscopic positive resection margin (i.e. R1 resection). Arrows: tumor cells with thermal artifact are present at the inked tissue edge. The lesion is an encapsulated follicular variant of papillary thyroid carcinoma.

Figure 4

Vascular invasion. Tumor emboli covered by endothelial cells are present within capsular vasculature (A), which may be associated with fibrin thrombus (B, arrow heads).

Figure 5

Common forms of capsular invasion. A: Hurthle cell carcinoma showing the typical mushroom like shape invasion (ci) into the full thickness of the capsule (c). Note the presence of a new fibrous capsule at the leading edge of the invasive tumor bud (arrow). B: Hurthle cell carcinoma in a different patient displaying capsular invasion in the form of a tumor nodule (ci) lying immediately outside an intact capsule (c). The point of entry into the capsule is not apparent at this particular level. This is not an uncommon finding.