Association of the Genomic Profile of Medullary Thyroid Carcinoma with Tumor Characteristics and Clinical Outcomes in an International Multicenter Study

Oncological features of sporadic vs. hereditary pediatric medullary thyroid cancer

PURPOSE

No genomic data have been put forth that prove beyond a shadow of doubt that sporadic medullary thyroid cancer (MTC) occurs in infancy, childhood, and/or adolescence.

METHODS

This was a retrospective comparative study of consecutive patients with MTC who had neck surgery at a tertiary center over a 30-year period.

RESULTS

Included were 1252 patients with MTC (337 hereditary and 915 sporadic), of whom 107 (8.5%) were operated before the age of 18 yrs. Only 4 (3.7%) of the 107 pediatric patients, aged 14, 16, 17 and 17 years, had sporadic MTC. These 4 patients, 3 of whom had been referred for completion surgery, revealed much larger thyroid tumors (medians of 20 mm vs. 1.5-5 mm) than the 103 pediatric patients with hereditary MTC. As for extrathyroid extension and nodal metastases, the 4 patients with sporadic MTC were more comparable to the 37 carriers of highest-risk mutations, 31 (84%) of whom were index patients with de novo disease, than to the 66 carriers of high-risk, intermediate-risk, or low-risk RET mutations (25-38% vs. 0-8%, and medians of 9-9.5 vs. 0 node metastases after dissection of more (medians of 72-91.5 vs. 4.5-9) nodes).

CONCLUSION

Sporadic MTC, arising rarely, if ever, below the age of 14 years, is exceptional in infancy and childhood, and infrequent in adolescence. At diagnosis, it is almost as widely metastatic as hereditary MTC of the highest-risk category which almost always, like sporadic MTC, presents as de novo disease.

Minor role of TP53 and TERT promoter mutations in medullary thyroid carcinoma: report of new cases and revision of the literature

PURPOSE

Aims of this study were to investigate the prevalence of TP53 and TERT mutations in Medullary Thyroid carcinoma (MTC) and their role in inducing aggressiveness in positive cases.

METHODS

We performed a literature search in PubMed to identify studies investigating the prevalence of TERT and TP53 mutations in MTC. We also included data on MTC cases (n = 193) obtained at our center and unpublished. The in-silico pathogenicity of the TP53 mutations has been evaluated by predictor tools.

RESULTS

We identified a total of 25 and 11 published papers: all together 1280 cases have been investigated for the presence of TP53 mutations and 974 for TERT promoter mutation. Twenty-five out of 1280 (2%) cases had a TP53 mutation while only 3/974 MTC cases (0.3%) have been found to be positive for TERT promoter mutations. Among all, we identified 19 different TP53 mutations that in 12 cases were demonstrated to have an in silico predicted high pathogenic role and a high impact on protein function. Three non-sense and 4 probably not damaging mutations were also reported. The pathogenic role of the TERT promoter mutations has been previously in vitro determined. No correlation between TP53 and/or TERT mutations and aggressiveness of MTC has been demonstrated.

CONCLUSION

The prevalence of TP53 and TERT promoter mutations is very low in MTC. The reported mutations are pathogenic in the majority of cases. Because of their rarity it is not possible to clarify if they play or not a role in the pathogenesis and/or aggressiveness of this specific thyroid tumor.

Transcriptomic Differences in Medullary Thyroid Carcinoma According to Grade

Medullary thyroid carcinoma (MTC) is a rare cancer derived from neuroendocrine C-cells of the thyroid. In contrast to other neuroendocrine tumors, a histological grading system was lacking until recently. A novel two-tier grading system based on the presence of high proliferation or necrosis is associated with prognosis. Transcriptomic analysis was conducted on 21 MTCs, including 9 high-grade tumors, with known mutational status, using the NanoString Tumor Signaling 360 Panel. This analysis, covering 760 genes, revealed upregulation of the genes EGLN3, EXO1, UBE2T, UBE2C, FOXM1, CENPA, DLL3, CCNA2, SOX2, KIF23, and CDCA5 in high-grade MTCs. Major pathways differentially expressed between high-grade and low-grade MTCs were DNA damage repair, p53 signaling, cell cycle, apoptosis, and Myc signaling. Validation through qRT-PCR in 30 MTCs demonstrated upregulation of ASCL1, DLL3, and SOX2 in high-grade MTCs, a gene signature akin to small-cell lung carcinoma, molecular subgroup A. Subsequently, DLL3 expression was validated by immunohistochemistry. MTCs with DLL3 overexpression (defined as ≥ 50% of positive tumor cells) were associated with significantly lower disease-free survival (p = 0.041) and overall survival (p = 0.01). Moreover, MTCs with desmoplasia had a significantly increased expression of DLL3. Our data supports the idea that DLL3 should be further explored as a predictor of aggressive disease and poor outcomes in MTC.

Medullary Thyroid Cancer: Molecular Drivers and Immune Cellular Milieu of the Tumour Microenvironment-Implications for Systemic Treatment

In this review, we explore the underlying molecular biology of medullary thyroid carcinoma (MTC) and its interplay with the host immune system. MTC is consistently driven by a small number of specific pathogenic variants, beyond which few additional genetic events are required for tumorigenesis. This explains the exceedingly low tumour mutational burden seen in most MTC, in contrast to other cancers. However, because of the low tumour mutational burden (TMB), there is a correspondingly low level of tumour-associated neoantigens that are presented to the host immune system. This reduces tumour visibility and vigour of the anti-tumour immune response and suggests the efficacy of immunotherapy in MTC is likely to be poor, acknowledging this inference is largely based on the extrapolation of data from other tumour types. The dominance of specific RET (REarranged during Transfection) pathogenic variants in MTC tumorigenesis rationalizes the observed efficacy of the targeted RET-specific tyrosine kinase inhibitors (TKIs) in comparison to multi-kinase inhibitors (MKIs). Therapeutic durability of pathway inhibitors is an ongoing research focus. It may be limited by the selection pressure TKI treatment creates, promoting survival of resistant tumour cell clones that can escape pathway inhibition through binding-site mutations, activation of alternate pathways, and modulation of the cellular and cytokine milieu of the tumour microenvironment (TME).

Primary resistance to selpercatinib in a patient with advanced medullary thyroid cancer

Selpercatinib, a selective RET kinase inhibitor, has demonstrated remarkable efficacy in treating patients with advanced medullary (MTC) and differentiated thyroid cancer with RET alterations. Primary resistance to selpercatinib is a very uncommon situation, and its underlying mechanisms are poorly understood. We report the case of a 42-year-old female with advanced MTC harboring a somatic M918T RET mutation who exhibited a primary resistance to selpercatinib. Despite prompt treatment initiation after the diagnosis of progressive disease, the patient continued experiencing rapid spread of disease, characterized by the appearance of new metastatic lesions and increased tumor burden. Genomic analysis revealed no additional mutations associated with on-target or off-target resistance. This case highlights a rare clinical scenario of primary resistance to selpercatinib in advanced MTC. While secondary resistance mechanisms have been well-documented, primary resistance remains poorly understood. Possible explanations include tumor heterogeneity and activation of alternative signaling pathways that stills need to be elucidated. Emerging therapies targeting resistance mechanisms and next-generation RET inhibitors offer promising avenues for further investigation.

Cytologic risk stratification of medullary thyroid carcinoma: Does it make the grade?

Recent efforts to develop a histologic grading system for medullary thyroid carcinoma is gaining broad acceptance. How well do these grading parameters translate to cytology specimens?