Detection of RET/PTC, TRK and BRAF mutations in preoperative diagnosis of thyroid nodules with indeterminate cytological findings

Perspectives for improved and more accurate classification of thyroid epithelial tumors

CONTEXT

Histologic examination of thyroid nodules is the current standard to distinguish benign from malignant thyroid epithelial tumors and to classify histologic subtypes. This review analyzes the problems in histological differential diagnosis as well as contradictions between histology and molecular data and describes possibilities to combine histology with molecular data in an effort to more accurately classify thyroid epithelial tumors.

EVIDENCE ACQUISITION

Published literature, addressing the current recommendations for thyroid tumor classification, as well as literature on the application of histology and molecular studies on the etiology of thyroid tumors is analyzed.

EVIDENCE SYNTHESIS

The current histologic criteria to classify thyroid tumors, especially follicular-patterned tumors, are hampered by considerable interobserver variability. The detection of somatic mutations via genotyping and the definition of potentially informative gene expression signatures by microarray analyses, which can distinguish cancer subtypes as well as low- and high-risk cohorts, have recently demonstrated significant diagnostic potential. Moreover, in a routine diagnostic setting, micro-RNA profiling appears most promising due to their relative stability and the high accuracy of their expression profiles.

CONCLUSIONS

It is very likely that molecular definitions of thyroid tumors mentioned in the current World Health Organization classification will be further developed, leading to future progress in defining thyroid tumor types by an integrated histologic and molecular approach. These integrated classifications need to be evaluated for their specific impact on thyroid tumor diagnosis and prognosis.

Genome-wide studies in thyroid neoplasia

There is much interest in the application of genome biology to the field of thyroid neoplasia, despite the relatively low mortality rate associated with thyroid cancer in general. The principal reason for this interest is that the field of thyroid neoplasia stands to benefit from the application of genomic information to address a variety of pathologic and clinical issues. In addition to practical patient care issues, there is an excellent opportunity of expand the basic understanding of thyroid carcinogenesis. In this article, the most relevant genomic work on thyroid tumors performed to date is reviewed along with some general comments about the potential impact of genomic biology on thyroid pathology and the management of patients with thyroid nodules and cancer.

Clinical implications of BRAF mutation in thyroid carcinoma

Significant progress has recently been made in the clinical management of papillary thyroid carcinoma. The accuracy of diagnosis and prognostic stratification of this type of carcinoma are high but still fall below 100%. Lack of effective treatments for advanced stage papillary thyroid carcinoma leads to death in some patients. Approximately half of all such carcinomas harbor mutations in the gene encoding the serine/threonine-kinase B-type Raf kinase (BRAF), resulting in constitutive activation of the mitogen-activated protein kinase-extracellular-signal-regulated kinases signal transduction pathway. There is intriguing evidence that BRAF mutation testing of papillary thyroid carcinoma might improve the diagnosis, prognostic stratification and treatment of these tumors but large, prospective trials are needed to define the actual clinical impact of these approaches.

What is New on Thyroid Cancer Biomarkers

Thyroid cancer harbours in about 5% of thyroid nodules. The majority of them are well-differentiated cancers originating from the follicular epithelium, and are subdivided into papillary and follicular carcinomas. Undifferentiated carcinomas and medullary thyroid carcinomas arising from C cells are less common.

Although most thyroid nodules are benign, distinguishing thyroid cancer from benign lesions is crucial for an appropriate treatment and follow-up. The fine needle aspiration cytology (FNAC) allows the diagnosis of nature of thyroid nodules in the majority of cases. However, FNAC has some limitations, particularly in the presence of follicular lesions which can appear dubious in rare instances even at histology.

In an effort to improve diagnostic accuracy and offer new prognostic criteria, several immunohistochemical and molecular markers have been proposed. However, most of them have to be validated on large series before being used in routine practice.

Orolabial signs are important clues for diagnosis of the rare endocrine syndrome MEN 2B. Presentation of two unrelated cases

Multiple endocrine neoplasia syndromes (MEN) are genetic disorders with glandular hyperplasia and consecutive malignant neoplasia. MEN type 2B is the least common form of these tumor syndromes. It presents with typical dysmorphic features, mucosal neuromas, ganglioneuromatosis, medullary thyroid carcinoma (MTC) and phaeochromocytoma. The prognosis depends on the presence of MTC. We have surprisingly found two unrelated patients with this syndrome at our department within two weeks. In the medical history of a 17-year-old boy, Crohn's disease had been considered because of abdominal pain and distention. He had marfanoid appearance and previously undergone minor surgeries for a large tongue with neuromas and hypertrophic gums. Two weeks later, a 10-year-old girl presented with a hard palpable mass on her neck. She had thickened lips, neuromas on the tongue and a solitary thyroid nodule. Genetic analysis was carried out in both patients and a heterozygous M918T mutation of the RET proto-oncogene was found. Laboratory tests and imaging studies were consistent with MTC. Phaeochromocytoma was not present. Both patients underwent total thyroidectomy and lymph node dissection. Histological examination confirmed the diagnosis of MTC. In conclusion, the initial diagnosis of MEN 2B should be suspected on the presence of typical facial/oral signs and gastrointestinal symptoms. Hormonal tests and imaging techniques of the thyroid and the adrenals can confirm the clinical diagnosis of MEN 2B and genetic analysis can prove its germline origin.

Cytological and molecular diagnosis of solid variant of papillary thyroid carcinoma: a case report

Papillary thyroid carcinoma (PTC) composed by predominant solid areas is diagnosed as a distinct variant on histological samples. Here we present a case of PTC recognized preoperatively by fine needle cytology as a solid variant. This diagnosis was made by combining cytology with the detection of the BRAF^VK600-1E mutation, the molecular hallmark of the solid variant of PTC. Histological and molecular evaluation of the surgical specimen confirmed this pre-operative diagnosis. Thus combining cytology to BRAF molecular analysis is useful to refine the cytological diagnosis of this variant also on FNC specimens.

Recent developments in the clinical application of thyroid cancer biomarkers

PURPOSE OF REVIEW

The aim of this article is to provide an update on the status of the clinical application of thyroid cancer biomarkers.

RECENT FINDINGS

Our understanding of the tumor cell biology of thyroid cancer of follicular cell origin has improved and modern genomic technological tools are providing new data that may have clinical ramifications. The common somatic genetic changes in thyroid cancer of follicular cell origin (RET/PTC, NTRK, RAS, BRAF, PAX8-PPARgamma) are generally mutually exclusive, with distinct genotype-histologic subtype of thyroid cancer and genotype-phenotype associations observed. Mutation analysis in thyroid nodule fine needle aspiration biopsy has been applied to improve the diagnostic accuracy of fine needle aspiration biopsy and cytologic examination. Gene expression profiling studies have identified numerous diagnostic biomarkers of thyroid cancer that are beginning to be applied in fine needle aspiration biopsy samples to improve diagnosis. The BRAF mutation has recently been shown to be associated with disease aggressiveness, and as an independent prognostic biomarker.

SUMMARY

There has been significant progress toward identifying biomarkers that could improve the accuracy of fine needle aspiration biopsy in the evaluation of patients with thyroid nodule and predicting disease aggressiveness. Future clinical trials evaluating the accuracy and cost-effectiveness of applying these biomarkers in the management of thyroid neoplasm should be considered.

Incidentally simultaneous occurrence of RET/PTC, H4-PTEN and BRAF mutation in papillary thyroid carcinoma

Because interaction existed between PTEN and RET-RAS-RAF-MAPK pathway, H4-PTEN (a newly identified gene rearrangement), RET/PTC and BRAF mutation were scanned in 125 Chinese patients with papillary thyroid carcinoma (PTC). H4-PTEN were detected in 9.6% of PTC and the frequency of the occurrence of BRAF mutation and/or RET/PTC in H4-PTEN positive tumors was extremely high (75%). On the other hand, age has an important effect on the aberration formation and young age renders more prone to multi-genetic events. A combinational scanning of these involved changes will improve the predictive value of molecular aberrations in the treatment of PTC.

Molecular detection of PPAR gamma rearrangements and thyroid carcinoma in preoperative fine-needle aspiration biopsies

The pathologic diagnosis of thyroid follicular tumors is difficult, particularly in preoperative fine-needle aspiration biopsies. To investigate whether the molecular diagnosis of PPAR gamma rearrangements can detect thyroid carcinomas in fine-needle aspiration biopsies, we performed interphase fluorescence in situ hybridization on 24 thyroid fine-needle aspiration and 17 follow-up thyroidectomy specimens. Two of the 24 fine-needle aspiration biopsies contained PPAR gamma rearrangements, and both were diagnosed suggestive of a thyroid follicular neoplasm by cytology. The two corresponding thyroidectomies each contained PPAR gamma rearrangements in all tumor cells and, both were diagnosed follicular-patterned thyroid carcinomas-one a follicular carcinoma and the other a follicular variant of papillary carcinoma, the latter by majority of expert endocrine pathologists. Our experiments demonstrate that PPAR gamma rearrangements can detect a subset of follicular-patterned thyroid carcinomas in preoperative thyroid fine-needle aspiration biopsies. The ultimate utility of mutations such as PPAR gamma rearrangements in diagnosis of thyroid carcinoma must be proven by direct correlation of mutation status with thyroid tumor biology and not just with thyroid tumor morphology, a subjective and imprecise marker of clinical behavior. The application of specific mutations to preoperative diagnosis of thyroid carcinoma is predicted to improve the accuracy and reduce the costs of treating patients with thyroid tumors.

A molecular expression signature distinguishing follicular lesions in thyroid carcinoma using preamplification RT-PCR in archival samples

Follicular variant of papillary thyroid carcinoma is a lesion that frequently causes difficulties from a diagnostic perspective in the laboratory. The purpose of this study was to interrogate a cohort of archival thyroid lesions using gene expression analysis of a panel of markers proposed to have utility as adjunctive markers in the diagnosis of thyroid neoplasia and follicular variant of papillary thyroid carcinoma in particular. Laser Capture Microdissection was used to procure pure cell populations for extraction. In addition a novel, multiplex preamplification technique was used to facilitate analysis of multiple targets. The panel comprised: HLA-DMA, HLA-DBQ1, CD74, CSNK1G2, IRF3, KRAS2, LYN, MT1K, MT1X, RAB23, TGFB1 and TOP2A, with CDKN1B as an endogenous control. Expression profiles for each target were generated using TaqMan Real-Time PCR. HLA-DMA, HLA-DQB1, MT1X, CSNK1G2 and RAB23 were found to be differentially expressed (P<0.05) when comparing follicular adenoma and follicular variant of papillary thyroid carcinoma. Comparison of follicular adenoma and follicular thyroid carcinoma groups showed significant differential expression for MT1K, MT1X and RAB23 (P<0.05). Comparison of the papillary thyroid carcinoma group (classic and follicular variants) and the follicular adenoma group showed differential expression for CSNK1G2, HLA-DQB1, MT1X and RAB23 (P<0.05). Finally, KRAS2 was found to be differentially expressed (P<0.05) when comparing the papillary thyroid carcinoma and follicular thyroid carcinoma groups. This panel of molecular targets discriminates between follicular adenoma, papillary thyroid carcinoma, follicular variant of papillary thyroid carcinoma and follicular thyroid carcinoma by their expression repertoires. It may have utility for broader use in the setting of fine-needle aspiration cytology and could improve the definitive diagnosis of certain categories of thyroid malignancy.