Germline and somatic mutations of the APC gene in papillary thyroid carcinoma associated with familial adenomatous polyposis: Analysis of three cases and a review of the literature

De novo familial adenomatous polyposis associated thyroid cancer with a c.2929delG frameshift deletion mutation in APC: a case report and literature review

BACKGROUND

Germline mutations in the APC gene located on chromosome 5q 21-22 can lead to familial adenomatous polyposis (FAP) and the development of colorectal cancer (CRC) if left untreated. As a rare extracolonic manifestation, thyroid cancer is diagnosed in about 2.6% of FAP patients. The genotype-phenotype correlation in FAP patients with thyroid cancer remains unclear.

CASE PRESENTATION

We present a 20-year-old female of FAP with thyroid cancer as the initial manifestation. The patient was asymptomatic and developed colon cancer liver metastases 2 years after the diagnosis of thyroid cancer. The patient underwent multiple surgical treatments in several organs, and regular colonoscopy with endoscopic polypectomy was performed. Genetic testing demonstrated the c.2929delG (p.Gly977Valfs*3) variant in exon 15 of the APC gene. This represents a previously undescribed APC mutation. This mutation causes loss of multiple structures on the APC gene including the 20-amino acid repeats, the EB1 binding domain, and the HDLG binding site, which may be pathogenic through β-catenin accumulation, cell cycle microtubule dysregulation, and tumor suppressor inactivation.

CONCLUSIONS

We report a de novo FAP case with thyroid cancer presenting atypically aggressive features harboring a novel APC mutation and review APC germline mutations in patients with FAP-associated thyroid cancer.

Looking at Thyroid Cancer from the Tumor-Suppressor Genes Point of View

Simple Summary

Thyroid cancer is the most common endocrine cancer. As tumor-suppressor genes (TSGs) are implicated in many different functions in the organism, their loss in cells in a normal tissue may drive their transformation into cancer cells. TSGs are generally classified into three subclasses: (i) gatekeepers that encode proteins involved in the control of cell cycle and apoptosis; (ii) caretakers that produce proteins implicated in maintaining genomic stability; and (iii) landscapers that, when mutated, create a suitable environment for neoplastic growth. Different inactivation mechanisms may suppress TSG function. Understanding these mechanisms and TSG alterations in thyroid tumors is of great importance for thyroid cancer prognosis, diagnosis, and therapy. The present review paper discusses TSG inactivation mechanisms and alterations in order to help to identify more efficient therapeutic modalities for thyroid cancer management.

Abstract

Thyroid cancer is the most frequent endocrine malignancy and accounts for approximately 1% of all diagnosed cancers. A variety of mechanisms are involved in the transformation of a normal tissue into a malignant one. Loss of tumor-suppressor gene (TSG) function is one of these mechanisms. The normal functions of TSGs include cell proliferation and differentiation control, genomic integrity maintenance, DNA damage repair, and signaling pathway regulation. TSGs are generally classified into three subclasses: (i) gatekeepers that encode proteins involved in cell cycle and apoptosis control; (ii) caretakers that produce proteins implicated in the genomic stability maintenance; and (iii) landscapers that, when mutated, create a suitable environment for malignant cell growth. Several possible mechanisms have been implicated in TSG inactivation. Reviewing the various TSG alteration types detected in thyroid cancers may help researchers to better understand the TSG defects implicated in the development/progression of this cancer type and to find potential targets for prognostic, predictive, diagnostic, and therapeutic purposes. Hence, the main purposes of this review article are to describe the various TSG inactivation mechanisms and alterations in human thyroid cancer, and the current therapeutic options for targeting TSGs in thyroid cancer.

Cribriform-Morular Thyroid Carcinoma Is a Distinct Thyroid Malignancy of Uncertain Cytogenesis

Tumors with papillary cribriform and morular architecture were initially considered to be variants of papillary thyroid carcinoma; however, recent observations have challenged this view. In this study, we reviewed the demographical, histopathological, and immunohistochemical features of the largest case series, consisting of 33 tumors. The age at time of pathological diagnosis ranged from 18 to 59 (mean 33) years, and all patients except one were female. Sixteen patients had multifocal and fifteen had unifocal disease. The status of focality was unavailable in two patients. Tumors were well-circumscribed, ranging in size from 0.1 to 8.0 cm. The cribriform component was admixed with morulae in the majority, except seven had a cribriform-predominant architecture and two had predominantly solid growth. Variable degrees of nuclear enlargement, elongation, overlapping, and grooves were seen but florid nuclear convolution, intranuclear pseudoinclusions, and optically clear nuclei due to chromatin margination were not appreciated. There was no or little colloid material within the cribriform spaces. Two solid tumors had high-grade features. Immunohistochemical studies showed beta-catenin nuclear and cytoplasmic positivity in all cases. The cribriform component was positive for TTF1 and negative for thyroglobulin. PAX8 was absent in half of these tumors and focal in the remainder. Morulae were positive for keratin 5 and CD5 and negative for p63, p40, TTF1, and PAX8. Molecular studies revealed germline APC mutations in 12 tumors and were negative in 5 sporadic tumors in a subset of tested tumors. Irrespective of the antibody used in this cohort, all cribriform-morular carcinomas express TTF1; however, PAX8 immunoreactivity is weak, focal or negative, and all tumors lack thyroglobulin reactivity; these findings raise questions about tumor cell origin and may indicate that these are not of thyroid follicular epithelial differentiation. We postulate that morulae may represent divergent thymic/ultimobranchial pouch-related differentiation. Given their unique cytomorphology, immunohistochemical profiles, and genetic features that have little overlap with traditional follicular cell-derived thyroid carcinomas, we propose that these tumors represent a distinct form of thyroid carcinoma unrelated to other neoplasms of thyroid follicular cells.

Multifocality in a Patient with Cribriform-Morular Variant of Papillary Thyroid Carcinoma Is an Important Clue for the Diagnosis of Familial Adenomatous Polyposis

Background: Cribriform-morular variant of papillary thyroid carcinoma (CMV-PTC) is a rare subtype of PTC, which occurrs predominantly in young women. This disease much more frequently presents in patients with familial adenomatous polyposis (FAP). FAP is an autosomal dominant inherited disease, which arises from germline mutations in the adenomatous polyposis coli (APC) gene. To clarify the distinctive clinical features of CMV-PTC, a comparison study was performed between familial types and sporadic types. Methods: Between 2007 and 2018, 15 CMV-PTC patients underwent thyroidectomy in Samsung Medical Center. The clinical features of these patients were retrospectively reviewed. Results: All patients were women with a median age of 26 years (range 17-46 years). The median maximum diameter was 1.0 cm (range 0.4-3.5 cm). All tumors underwent immunostaining and showed nuclear and/or cytoplasmic staining for β-catenin. On ultrasonography, most nodules had benign-looking features (well-defined, hypoechoic, and oval to round shapes without calcification), but a few nodules had capsular invasion and taller than wide shape. On preoperative fine-needle aspiration cytology, five patients (33%) were diagnosed as CMV-PTC, nine (60%) as PTC, but one (7%) as follicular neoplasm or PTC-follicular variant. Six patients (40%) had FAP, and four of them had total colectomy due to FAP. Five of them had a family history of FAP or colon cancer, or thyroid cancer. Germline mutations in the APC gene were found in all six patients with CMV-PTC associated with FAP, and five of them had de novo mutations. All patients with FAP-associated CMV-PTC had multiple tumors. All CMV-PTC patients had excellent response to initial therapy. Conclusions: Because of the association between FAP or colon cancer with multifocal CMV-PTC, we confirm that mutational analysis of the APC gene and colonoscopy should be carried out in these patients when multiple thyroid tumors are found.

Cribriform-Morular Variant of Papillary Thyroid Carcinoma With Poorly Differentiated Features: A Case Report With Immunohistochemical and Molecular Genetic Analysis

Cribriform-morular variant of papillary thyroid carcinoma (CMVPTC) is usually an inherited malignancy and may be a presenting indicator of familial adenomatous polyposis syndrome although it may occasionally be sporadic. Known CMVPTC mutations include adenomatous polyposis coli ( APC) and β-catenin ( CTNNB1) genes. Despite its malignant classification, CMVPTC is considered to be a well-differentiated thyroid tumor with a generally good behavior. In contrast, poorly differentiated thyroid carcinoma is an aggressive tumor. We report a case of CMVPTC with poorly differentiated features in a young female without phenotypic features of familial adenomatous polyposis but with known germline alterations of the APC gene. High throughput sequencing showed germline chromosome 5q deletion encompassing the APC gene in all components with additional unique genetic alterations in the somatic components. A single nucleotide substitution (c.1548+1G>A, NM_000038.5) located one base pair downstream of exon 12 of the APC gene was identified in the CMVPTC component, and a pathogenic frameshift deletion in exon 14 of APC (c.3642del, p.Ser1214Argfs*51, NM_000038.5) was identified in the poorly differentiated thyroid carcinoma component. No other cancer-associated genes were identified by our techniques. Our case represents a rare phenomenon of poorly differentiated features in association with CMVPTC. To our knowledge, ours is the only such report of poorly differentiated features arising in association with an inherited CMVPTC.

Cribriform-morular variant of thyroid carcinoma: a neoplasm with distinctive phenotype associated with the activation of the WNT/β-catenin pathway

Cribriform-morular variant of thyroid carcinoma is classically associated with familial adenomatous polyposis but, it can also occur as a sporadic neoplasm. This neoplasm is much more frequently observed in women than in men (ratio of 61:1). In familial adenomatous polyposis patients, tumors are generally multifocal and/or bilateral (multinodular appearance), whereas in the sporadic cases tumors tend to occur as single nodules. The tumors are well delimited, and characteristically show a blending of follicular, cribriform, papillary, trabecular, solid, and morular patterns. Neoplastic cells are tall or cuboidal with the occasional nuclear features of classic papillary thyroid carcinoma. The morules include cells with peculiar nuclear clearing and show positivity for CDX2 and CD10. Angioinvasion and capsular invasion have been described in about 30 and 40% of cases, respectively, with lymph node metastases in less than 10% of patients and distant metastases in 6%. Although this tumor has good prognosis, neuroendocrine and/or poor differentiation have been associated with aggressive behavior. Tumor cells can be focally positive or negative for thyroglobulin, but are always positive for TTF-1, estrogen and progesterone receptors, and negative for calcitonin and cytokeratin 20. Nuclear and cytoplasmic staining for β-catenin is the hallmark of this tumor type; this feature plays a role in fine needle aspiration biopsy. Cribriform-morular variant of thyroid carcinoma has a peculiar endodermal (intestinal-like) type phenotype, activation of the WNT/β-catenin signaling pathway, and belongs to the non-BRAF-non-RAS subtype of the molecular classification of thyroid tumors. Elevated expression of estrogen and progesterone receptors and activation of the WNT/β-catenin pathway may prove useful as putative therapeutic targets in cases that do not respond to conventional therapy. Clinicians should be alerted to the possibility of familial adenomatous polyposis when a diagnosis of cribriform-morular variant of thyroid carcinoma is made. Instead of being considered as a variant of papillary thyroid carcinoma its designation as cribriform-morular thyroid carcinoma seems more appropriate.

Inherited variants in genes somatically mutated in thyroid cancer

Background

Tumour suppressor genes when mutated in the germline cause various cancers, but they can also be somatically mutated in sporadic tumours. We hypothesized that there may also be cancer-related germline variants in the genes commonly mutated in sporadic well-differentiated thyroid cancer (WDTC).

Methods

We performed a two-stage case-control association study with a total of 2214 cases and 2108 healthy controls from an Italian population. By genotyping 34 single nucleotide polymorphisms (SNPs), we covered a total of 59 missense SNPs and SNPs located in the 5' and 3' untranslated regions (UTRs) of 10 different genes.

Results

The Italian1 series showed a suggestive association for 8 SNPs, from which three were replicated in the Italian2 series. The meta-analysis revealed a study-wide significant association for rs459552 (OR: 0.84, 95%CI: 0.75–0.94) and rs1800900 (OR: 1.15, 95%CI: 1.05–1.27), located in the APC and GNAS genes, respectively. The APC rs459552 is a missense SNP, located in a conserved amino acid position, but without any functional consequences. The GNAS rs1800900 is located at a conserved 5'UTR and according to the experimental ENCODE data it may affect promoter and histone marks in different cell types.

Conclusions

The results of this study yield new insights on WDTC, showing that inherited variants in the APC and GNAS genes can play a role in the etiology of thyroid cancer. Further studies are necessary to better understand the role of the identified SNPs in the development of WDTC and to functionally validate our in silico predictions.

Developmental pathways associated with cancer metastasis: Notch, Wnt, and Hedgehog

Master developmental pathways, such as Notch, Wnt, and Hedgehog, are signaling systems that control proliferation, cell death, motility, migration, and stemness. These systems are not only commonly activated in many solid tumors, where they drive or contribute to cancer initiation, but also in primary and metastatic tumor development. The reactivation of developmental pathways in cancer stroma favors the development of cancer stem cells and allows their maintenance, indicating these signaling pathways as particularly attractive targets for efficient anticancer therapies, especially in advanced primary tumors and metastatic cancers. Metastasis is the worst feature of cancer development. This feature results from a cascade of events emerging from the hijacking of epithelial-mesenchymal transition, angiogenesis, migration, and invasion by transforming cells and is associated with poor survival, drug resistance, and tumor relapse. In the present review, we summarize and discuss experimental data suggesting pivotal roles for developmental pathways in cancer development and metastasis, considering the therapeutic potential. Emerging targeted antimetastatic therapies based on Notch, Wnt, and Hedgehog pathways are also discussed.

Regulation of CTNNB1 signaling in gastric cancer and stem cells

Recent research has shown that the alteration of combinations in gene expression contributes to cellular phenotypic changes. Previously, it has been demonstrated that the combination of cadherin 1 and cadherin 2 expression can identify the diffuse-type and intestinal-type gastric cancers. Although the diffuse-type gastric cancer has been resistant to treatment, the precise mechanism and phenotypic involvement has not been revealed. It may be possible that stem cells transform into gastric cancer cells, possibly through the involvement of a molecule alteration and signaling mechanism. In this review article, we focus on the role of catenin beta 1 (CTNNB1 or β-catenin) and describe the regulation of CTNNB1 signaling in gastric cancer and stem cells.