Emerging Biomarkers in Thyroid Practice and Research

Abstract

Thyroid cancer is the most common endocrine malignancy. Recent developments in molecular biological techniques have led to a better understanding of the pathogenesis and clinical behavior of thyroid neoplasms. This has culminated in the updating of thyroid tumor classification, including the re-categorization of existing and introduction of new entities. In this review, we discuss various molecular biomarkers possessing diagnostic, prognostic, predictive and therapeutic roles in thyroid cancer. A comprehensive account of epigenetic dysregulation, including DNA methylation, the function of various microRNAs and long non-coding RNAs, germline mutations determining familial occurrence of medullary and non-medullary thyroid carcinoma, and single nucleotide polymorphisms predisposed to thyroid tumorigenesis has been provided. In addition to novel immunohistochemical markers, including those for neuroendocrine differentiation, and next-generation immunohistochemistry (BRAF V600E, RAS, TRK, and ALK), the relevance of well-established markers, such as Ki-67, in current clinical practice has also been discussed. A tumor microenvironment (PD-L1, CD markers) and its influence in predicting responses to immunotherapy in thyroid cancer and the expanding arena of techniques, including liquid biopsy based on circulating nucleic acids and plasma-derived exosomes as a non-invasive technique for patient management, are also summarized.

Keywords: diagnosis; immunohistochemistry; liquid biopsy; molecular; predictive biomarkers; prognosis; targeted therapy; thyroid cancer; tumor microenvironment.

Figure 1

Frequency and pattern of genetic alterations across thyroid tumors. The heatmap depicts the frequency of non-synonymous mutations, deletions and fusions in selected genes, and copy number alterations (CNA). NH, nodular hyperplasia; FA, follicular adenoma; OA, oncocytic adenoma; NIFTP, non-invasive follicular thyroid neoplasm with papillary-like nuclear features; HTT, hyalinizing trabecular tumor; FTC, follicular thyroid carcinoma; OCA, oncocytic carcinoma; PTC, papillary thyroid carcinoma; OCA, oncocytic carcinoma; PDTC, poorly differentiated thyroid carcinoma; ATC, anaplastic thyroid carcinoma; MTC, medullary thyroid carcinoma; and HMT, histone methyltransferase. References for information used in this figure can be found in Table S1.

Figure 2

Genetic evolution of differentiated thyroid cancers. PTC, papillary thyroid carcinoma; FTC, follicular thyroid carcinoma; OCA, oncocytic carcinoma; and ATC, anaplastic thyroid carcinoma.

Figure 3

Diagnostic performance of commercially available molecular panels for thyroid nodules with indeterminate FNA cytology (atypia of undetermined significance/follicular lesion of undetermined significance and follicular neoplasm/suspicious for a follicular neoplasm). The length of the error bars is a 95% confidence interval. These data were obtained from clinical validation studies of Afirma Gene Sequencing Classifier (GSC) [118], ThyroSeq v3 Genomic Classifier (GC) [119], ThyGeNEXT and ThyraMIR [117], and RosettaGX Reveal [120]. NIFTP, non-invasive follicular thyroid neoplasm with papillary-like nuclear features; NPV, negative predictive value; and PPV, positive predictive value.

Figure 4

Immunohistochemical staining for Ki-67 in thyroid tumors. Different Ki-67 labeling indices are observed in follicular adenoma (a, 2%), follicular thyroid carcinoma (b, 4%), papillary thyroid carcinoma (c, 5%), poorly differentiated thyroid carcinoma (d, 20%), and high-grade papillary thyroid carcinoma (e, 35%) coexisting with anaplastic thyroid carcinoma (f, 40%). ×400 (a–f). Scale bar = 50 μm.

Figure 5

Immunohistochemical detection of mutations in thyroid cancer. (a) BRAF VE1 immunostaining in papillary thyroid carcinoma (PTC) with BRAF V600E mutation. (b) Pan-TRK immunostaining in PTC with RBPMS-NTRK3 fusion. (c) Cribriform morular thyroid carcinoma showing nuclear expression of β-catenin. (d) ALK immunostaining in PTC with EML4-ALK fusion. ×400 (a–d). Scale bar = 50 μm.

Figure 6

PD-L1 expression in papillary thyroid carcinoma. (a) Diffuse expression of PD-L1 on tumor cells (×100). (b) A high-power view shows the membranous staining for PD-L1 in cancer cells (×400). Scale bar = 50 μm.

Figure 7

Immunohistochemical expression of CD markers by the thyroid cancer cells. CD10 expression in papillary thyroid carcinoma (PTC, a) and anaplastic thyroid carcinoma (b), CD15 expression in PTC (c), CD20 expression in PTC (d), loss of CD56 expression in PTC (e), and CD73 expression in PTC (f). ×400 (a–d,f). ×200 (e). Scale bar = 50 μm.