Macrofollicular Variant of Follicular Thyroid Carcinoma (MV-FTC) with a Somatic DICER1 Gene Mutation: Case Report and Review of the Literature

Distinctive role of DICER1 mutations in distant metastatic thyroid cancer

Objective

This study investigated the clinical significance of DICER1 mutations in patients with distant metastatic follicular cell-derived thyroid cancer (FDTC).

Methods

This study included 310 Chinese patients with distant metastatic FDTC. We analyzed the interactions between DICER1 mutations and other gene alterations and compared the clinicopathological characteristics of patients with pathogenic (P) or likely pathogenic (LP) DICER1 mutations (n=9), other gene alterations (n=253), and no gene alterations (n=37). To compare FDTCs with different drivers, isolated BRAFV600E, RAS mutations, and RET fusions were compared with isolated DICER1 mutations.

Results

The prevalence of DICER1 mutations was 6.5% (20/310) in the patient cohort. Among patients with DICER1 mutations, 45% (9/20) harbored P or LP DICER1 variants and 55% (11/20) harbored DICER1 variants of uncertain significance (VUS). The coexistence of DICER1 mutations and other gene alterations was detected in 65% (13/20) of patients. Compared with VUS, P or LP DICER1 variants were almost mutually exclusive with early driver alterations (such as BRAFV600E) (11.1% vs. 81.8%, P=0.002) and more coexisted with late-hit events, particularly TP53 mutations (44.4% vs. 27.3%, P=0.642). Clinically, compared with the no alteration and other alteration groups, the DICER1 mutation group exhibited larger primary tumors, higher poorly differentiated thyroid cancer proportion, more extrathyroidal extension, more extrapulmonary metastases, and higher radioactive iodine-refractory proportion (all P<0.05). Cases with isolated DICER1 mutations differed from those with isolated BRAFV600E and RET fusions in terms of tumor size, poorly differentiated thyroid cancer proportion, and metastatic sites, but were similar to cases with isolated RAS mutations in the high proportion of follicular thyroid cancer, N0, and extrapulmonary metastases.

Conclusions

Mutation of DICER1 gene is a non-negligible molecular event and it may represent an aggressive subset of FDTCs. DICER1 has RAS-like clinical characteristics and DICER1-mutant tumors exhibit more aggressive clinical behaviors compared with those with BRAFV600E and RET fusions.

MicroRNA regulator gene mutations in thyroid follicular nodular disease and thyroid cancer: does it all come down to timing?

In recent years, germline mutations in the microRNA (miRNA) processor genes DICER1 and DGCR8 have been coupled to the development of thyroid follicular nodular disease (TFND), thereby casting new light on the etiology of this enigmatic, benign condition in non-iodine-deficient regions. Moreover, DICER1 and DGCR8 mutations have also been reported in rare subsets of follicular cell-derived thyroid carcinomas. Specifically, truncating germline or missense somatic DICER1 mutations have been reported in small subsets of pediatric and adolescent follicular thyroid carcinoma (FTC) and poorly differentiated thyroid carcinoma (PDTC). Similarly, a recurrent somatic mutation of the DGCR8 gene has been observed in highly aggressive FTCs and in some indolent cases of encapsulated follicular variant of papillary thyroid carcinoma. The reason why identical mutations in the same miRNA processor gene can lead to such a myriad of thyroid conditions, ranging from benign TFND to FTCs and PDTCs, remains unclear. This review highlights key features of miRNA regulator gene mutations in thyroid disease and explores their potential roles as drivers or progression events in tumor development.

Atrophic changes in thyroid tumors are strong indicators of underlying DICER1 mutations: a bi-institutional genotype-phenotype correlation study

Somatic and biallelic DICER1 mutations are reported in subsets of thyroid tumors, supporting the role of this gene in thyroid tumor development. As recent studies have brought attention to macrofollicular patterns, atrophic changes, and papillary structures as being associated with DICER1 mutations, we sought to explore these observations in a bi-institutional cohort. A total of 61 thyroid lesions (54 tumors and 7 cases of thyroid follicular nodular disease; TFND), including 26 DICER1 mutated and 35 DICER1 wildtype controls were subjected to histological re-investigation and clinical follow-up. DICER1-mutated lesions showed a statistically significant association with younger age at surgery (29.2 ± 12.5 versus 51.3 ± 18.8, p = 0.0001), a predominant macrofollicular growth pattern (20/26 mutated cases versus 18/35 wildtype; p = 0.01) and atrophic changes (20/26 mutated cases versus 2/35 wildtype; p = 0.0001). Similar results were obtained when excluding TFND cases. We also present clinical and histological triaging criteria for DICER1 sequencing of thyroid lesions, which led to the identification of DICER1 variants in 16 out of 26 cases (62%) when followed. Among these, 3 out of 12 cases with available data were found to carry a constitutional DICER1 mutation. This observation suggests that the majority of DICER1 mutations are somatic-however implies that sequencing of constitutional tissues could be clinically motivated. We conclude that DICER1 mutations are amassed in younger patients with macrofollicular-patterned tumors and, most strikingly, atrophic changes. Given the rate of constitutional involvement, our findings could be of clinical value, allowing the pathologist to triage cases for genetic testing based on histological findings.

Overview of the 2022 WHO Classification of Familial Endocrine Tumor Syndromes

This review of the familial tumor syndromes involving the endocrine organs is focused on discussing the main updates on the upcoming fifth edition of the WHO Classification of Endocrine and Neuroendocrine Tumors. This review emphasizes updates on histopathological and molecular genetics aspects of the most important syndromes involving the endocrine organs. We describe the newly defined Familial Cancer Syndromes as MAFA-related, MEN4, and MEN5 as well as the newly reported pathological findings in DICER1 syndrome. We also describe the updates done at the new WHO on the syndromic and non-syndromic familial thyroid diseases. We emphasize the problem of diagnostic criteria, mention the new genes that are possibly involved in this group, and at the same time, touching upon the role of some immunohistochemical studies that could support the diagnosis of some of these conditions. As pathologists play an important role in identifying tumors within a familial cancer syndrome, we highlight the most important clues for raising the suspicious of a syndrome. Finally, we highlight the challenges in defining these entities as well as determining their clinical outcome in comparison with sporadic tumors. Instead of the usual subject review, we present the highlights of the updates on familial cancer syndromes by answering select questions relevant to practicing pathologists.

Expanding the spectrum of thyroid carcinoma with somatic DICER1 mutation: a survey of 829 thyroid carcinomas using MSK-IMPACT next-generation sequencing platform

DICER1 gene encodes an RNaseIII endoribonuclease essential for the cleavage of pre-microRNA to mature microRNA. Germline DICER1 mutation results in DICER syndrome, a cancer predisposition syndrome which manifests in the thyroid gland as early-onset multinodular goiter and increased risk for differentiated thyroid carcinoma. Recently, somatic DICER1 mutations were described in various thyroid neoplasms, including follicular adenoma, papillary thyroid carcinoma, follicular carcinoma, and poorly differentiated thyroid carcinoma. In this study, we identified and described 14 cases (1.7%) with somatic DICER1 mutations from a cohort of 829 patients with thyroid follicular cell-derived thyroid carcinomas which were sequenced using MSK-IMPACT targeted next-generation sequencing platform. We expanded the histologic spectrum of thyroid carcinomas with somatic DICER1 mutations to include Hurthle cell carcinoma, high-grade differentiated thyroid carcinoma, and anaplastic thyroid carcinoma. All patients were adults with a median age of diagnosis of 59 years (range: 22-82). Although rare, a subset of thyroid cancers, including the aggressive subtypes, display somatic DICER1 mutations, some of which have oncogenic potential.

Macrofollicular variant follicular thyroid tumors are DICER1 mutated and exhibit distinct histological features

AIMS

DICER1 germline mutations cause DICER1 syndrome, in which multinodular goitre is a common feature. Recently, somatic DICER1 mutations have been reported in sporadic thyroid carcinomas, of which the newly described macrofollicular variant of follicular thyroid carcinoma (MV-FTC) seems particularly enriched for this aberrancy. We report here histological and genetic findings in five follicular thyroid tumours with macrofollicular architecture (four carcinomas and one adenoma).

METHODS AND RESULTS

We have diagnosed five cases during a year-long period at the Karolinska University Hospital, a tertiary thyroid cancer center with a catchment area of approximately 2.3 million inhabitants. Tumour DNA was interrogated using a commercially available massive parallel sequencing platform. All cases were female patients, ranging from 13 to 33 years at surgery. A single patient was a DICER1 syndrome carrier; the others were sporadic cases. All tumours displayed a macrofollicular architecture with a broad capsule. The MV-FTCs displayed capsular invasion, but never vascular invasion. Areas with degenerative changes (microinfarctions) were noted in all cases, and focal papillary growth was observed in the majority. The Ki-67 proliferation index was always above 4%. All cases displayed DICER1 gene mutations, of which four of five cases displayed RNase IIIb hot-spot missense mutations adjoined by a second, deleterious variant in three of five tumouurs.

CONCLUSIONS

Macrofollicular variants of follicular thyroid tumours are predominantly found in younger females and are strongly linked to somatic DICER1 gene mutations. Histological features such as a broad tumorous capsule, focal infarctions and areas with papillae could constitute clues prompting further genetic analyses.