Circulating miR-26b-5p and miR-451a as diagnostic biomarkers in medullary thyroid carcinoma patients

PURPOSE/METHODS

The determination of tumour biomarkers is paramount to advancing personalized medicine, more so in rare tumours like medullary thyroid carcinoma (MTC), whose diagnosis is still challenging. The aim of this study was to identify non-invasive circulating biomarkers in MTC. To achieve this goal, paired MTC tissue and plasma extracellular vesicle samples were collected from multiple centres and microRNA (miRNA) expression levels were evaluated.

RESULTS

The samples from a discovery cohort of 23 MTC patients were analysed using miRNA arrays. Lasso logistic regression analysis resulted in the identification of a set of circulating miRNAs as diagnostic biomarkers. Among them, miR-26b-5p and miR-451a, were highly expressed and their expression decreased during follow-up in disease-free patients in the discovery cohort. Circulating miR-26b-5p and miR-451a were validated using droplet digital PCR in a second independent cohort of 12 MTC patients.

CONCLUSION

This study allowed the identification and validation of a signature of two circulating miRNAs, miR-26b-5p and miR-451a, in two independent cohorts reporting a significant diagnostic performance for MTC. The results of this study offer advancements in molecular diagnosis of MTC proposing a novel non-invasive tool to use in precision medicine.

BRAF K601E Mutation in Oncocytic Carcinoma of the Thyroid: A Case Report and Literature Review

BACKGROUND

Thyroid carcinoma (TC) is the most common endocrine cancer, with papillary thyroid carcinoma (PTC) being the most common subtype. BRAF and RAS oncogene were characterized as the most frequently altered genes in PTC, with a strong association between genotype and histotype. The most common mutation in BRAF gene is V600E and is prevalent in classic and aggressive variants of PTC, while BRAF K601E mutation is the most common among the other rare BRAF mutations. BRAF K601E mutated thyroid carcinomas are usually characterized by low aggressiveness, except for anecdotal cases of poorly differentiated TC.

CASE PRESENTATION

We described a case of oncocytic carcinoma of the thyroid (OCA) with an aggressive clinical course, including widespread metastasis and resistance to radioiodine treatment. Molecular analysis revealed the exclusive presence of the BRAF K601E mutation in both primary tumor and metastatic lesions. Accordingly, a revision of the literature about aggressive TC cases carrying BRAF K601E mutation was performed.

CONCLUSION

Although rare, this case emphasizes the relevance of considering BRAF K601E mutation in advanced non-PTC thyroid carcinomas, since it can be considered an actionable mutation for target therapies.

Chromosomal alterations in sporadic medullary thyroid carcinoma and correlation with outcome

Somatic Copy Number Alterations (SCNA) involving either a whole chromosome or just one of the arms, or even smaller parts have been described in about 88% of human tumors. This study investigated the SCNA profile in 40 well-characterized sporadic medullary thyroid carcinomas by comparative genomic hybridization array. We found that 26/40(65%) cases had at least one SCNA. The prevalence of SCNA, and in particular of chromosome 3 and 10, was significantly higher in cases with a RET somatic mutation. Similarly, SCNA of chromosomes 3, 9, 10 and 16 were more frequent in cases with a worse outcome and an advanced disease. By the pathway enrichment analysis, we found a mutually exclusive distribution of biological pathways in metastatic, biochemically persistent and cured patients. In particular, we found gain of regions involved in the intracellular signaling and loss of regions involved in DNA repair and TP53 pathways in the group of metastatic patients. Gain of regions involved in cell cycle and senescence were observed in patients with biochemical disease. Finally, gain of regions associated to the immune system and loss of regions involved in the apoptosis pathway were observed in cured patients suggesting a role of specific SCNA and corresponding altered pathways in the outcome of sporadic MTC.

NF1 Gene Inactivation Acts as Tumor Driver in RET/RAS Negative Medullary Thyroid Carcinomas

OBJECTIVE

20% of sporadic MTC has no RET/RAS somatic alterations or other known gene alterations. Aim of this study was to investigate RET/RAS negative MTC for the presence of NF1 alterations.

METHODS

we studied 18 sporadic RET/RAS negative MTC cases: Next generation sequencing of tumoral and blood DNA was performed using a custom panel including the entire coding region of the NF1 gene. The effect of NF1 alterations on the transcripts were characterized by RT-PCR and the loss of heterozygosity of the other NF1 allele was investigated with Multiplex Ligation-dependent Probe Amplification.

RESULTS

Two cases showed bi-allelic inactivation of NF1 with a prevalence of about 11% of RET/RAS negative cases. In a patient affected by neurofibromatosis there was a somatic intronic point mutation determining the transcript alteration in one allele and a germline loss of heterozygosity (LOH) in the other. In the other case described both the point mutation and the LOH were somatic events; this latter finding shows, for the first time, a driver role of NF1 inactivation in MTC independent of RET/RAS alterations and the presence of neurofibromatosis.

CONCLUSIONS

About 11% of our series of sporadic RET/RAS negative MTC harbor biallelic inactivation of NF1 suppressor gene also regardless neurofibromatosis status. According to our results, NF1 alterations should be searched in all RET/RAS negative MTC as possible driver. Moreover, this finding reduces the number of negative sporadic MTCs and may have important clinical implications in the management of these tumors.

Clinical evolution of sporadic medullary thyroid carcinoma with biochemical incomplete response after initial treatment

CONTEXT

The clinical response after surgery is a determinant in the management of patients with medullary thyroid carcinoma (MTC). In case of excellent or structural incomplete response, the follow-up strategies are well designed. Conversely, in case of biochemical incomplete response (BiR) the management is not clearly defined.

PURPOSE

To evaluate the overall and per-site prevalence of structural disease detection in sporadic MTC patients with BiR and to assess the predictive value of various clinical, biochemical, and genetics features.

METHODS

We evaluated data of 599 consecutive patients surgically treated for sporadic MTC (2000-2018) and followed-up at Endocrine Unit of the University Hospital of Pisa.

RESULTS

After a median of 5 months from surgery, 145/599 (24.2%) patients were classified as BiR. Structural disease was detected in 64/145 (44.1%), after a median time of 3.3 years. In 73.6% structural disease was detected at a single site, prevalently cervical lymph nodes. Among several others, at the time of first evaluation after surgery, only basal calcitonin (bCTN) and stage IVa/b were independent predictive factors. Also, structural disease was more frequent in patients with shorter CTN doubling time and somatic RET mutation.

CONCLUSIONS

In sporadic MTC patients with BiR the risk of detection of structural disease was about 50% at 10 years. Higher bCTN levels and staging predicted the risk of detecting structural disease. According to these findings, a stricter follow-up should be reserved to MTC with BiR and elevated values of bCTN and to those with an advanced stage. Long follow-up should anyway be considered for all BiR patients since 50% of them develop structural disease within 10 years.

Pre- and Post-operative Circulating Tumoral DNA in Patients With Medullary Thyroid Carcinoma

CONTEXT

Measurement of driver mutations in circulating tumoral DNA (ctDNA) obtained by liquid biopsy has been shown to be a sensitive biomarker in several human tumors.

OBJECTIVE

The aim of this study was to evaluate the clinical relevance of pre- and post-operative ctDNA in sporadic medullary thyroid cancer (sMTC).

METHODS

We studied pre- and post-operative ctDNA in 26 and 23 sMTC patients, respectively. ctDNA results were correlated to serum calcitonin (Ct), carcinoembryonic antigen (CEA), and other clinical/pathological features.

RESULTS

Twenty-six of 29 (89.7%) sMTCs were mutated either for RET or RAS and 3/29 (10.3%) were negative. Four of 26 (15.4%) cases showed positive pre-operative ctDNA with a significantly higher presence of RET M918T mutation (P = 0.0468). Patients with positive pre-operative ctDNA showed a higher variation allele frequency value of the somatic driver mutation (P = 0.0434) and a higher frequency of persistent disease (P = 0.0221). Post-operative ctDNA was positive only in 3/23 (13%) sMTCs and no one was positive for pre-operative ctDNA. Higher values of both Ct (P = 0.0307) and CEA (P = 0.0013) were found in positive ctDNA cases. Finally, the 7 cases harboring either pre- or post-operative positive ctDNA had a persistent disease (P = 0.0005) showing a higher post-operative serum Ct when compared with cases with negative ctDNA (P = 0.0092).

CONCLUSIONS

Pre-operative ctDNA in medullary thyroid cancer is not useful for diagnostic purposes, but it can be useful for predicting the outcome of the disease. In our series, post-operative ctDNA showed a potential for monitoring the response to therapies, but further studies are required to confirm our results.

Somatic RET Indels in Sporadic Medullary Thyroid Cancer: Prevalence and Response to Selpercatinib

CONTEXT

Although the majority of RET alterations are single nucleotide variants (SNV), small deletions and/or insertions have been reported at variable prevalence. No information about the efficacy of RET-specific inhibitors in patients harboring RET indels has been provided.

OBJECTIVE

We present an update on the prevalence of RET indels in medullary thyroid cancer (MTC) and describe the efficacy of selpercatinib in patients with advanced MTC with RET indels.

METHODS

The MTC tissues of 287 patients were analyzed using an Ion S5 targeted sequencing. The functional role of the reported indels have been evaluated by MutationTaster. Clinical and pathological data of MTC patients harboring a RET indel were collected and analyzed. Two patients with a RET indel were treated with selpercatinib.

RESULTS

Among 178 RET-positive cases, 147 (82.6%) harbored a SNV and 31 (17.4%) a RET in-frame indel. Nine indels were not previously reported and were found to be disease causing by MutationTaster. Patients harboring an indel were found to have an aggressive disease and 2 of them were treated with selpercatinib, experiencing a good response to the treatment.

CONCLUSION

These data show that RET indels are not infrequent and correlate with an aggressive disease. Two RET indel-positive patients showed a partial response to the treatment with a highly selective RET inhibitor; thus, these RET indels can be considered actionable mutations. In order to not miss these alterations, the analysis of the full gene is recommended.

Active Surveillance in RET Gene Carriers Belonging to Families with Multiple Endocrine Neoplasia

Simple Summary

MEN2 has a very high penetrance for the development of medullary thyroid cancer. However, intra- and inter-familial variabilities have been described. Accordingly, in this precision medicine era, a personalized approach should be adopted in subjects harboring RET mutations. In these subjects, we showed that thyroid surgery could be safely timed according to basal and stimulated calcitonin, especially in children who can reach adulthood, avoiding the risks of thyroid surgery and decreasing the period of a long-life hypothyroidism treatment.

Abstract

Multiple Endocrine Neoplasia 2 (MEN2) is a hereditary cancer syndrome for developing medullary thyroid cancer (MTC) due to germline mutations of RET gene. Subjects harboring a germline RET mutation without any clinical signs of MTC are defined as gene carriers (GCs), for whom guidelines propose a prophylactic thyroid surgery. We evaluate if active surveillance of GCs, pursuing early thyroid surgery, can be safely proposed and if it allows safely delaying thyroid surgery in children until adolescence/adulthood. We prospectively followed 189 GCs with moderate or high risk germline RET mutation. Surgery was planned in case of: elevated basal calcitonin (bCT) and/or stimulated CT (sCT); surgery preference of subjects (or parents, if subject less than 18 years old); other reasons for thyroid surgery. Accordingly, at RET screening, we sub-grouped GCs in subjects who promptly were submitted to thyroid surgery (Group A, n = 67) and who were not (Group B, n = 122). Group B was further sub-grouped in subjects who were submitted to surgery during their active surveillance (Group B1, n = 22) and who are still in follow-up (Group B2, n = 100). Group A subjects presented significantly more advanced age, bCT and sCT compared to Group B. Mutation RET^V804M was the most common variant in both groups but it was significantly less frequent in Group A than B. Analyzing age, bCT, sCT and genetic landscape, Group B1 subjects differed from Group B2 only for sCT at last evaluation. Group A subjects presented more frequently MTC foci than Group B1. Moreover, Group A MTCs presented more aggressive features (size, T and N) than Group B1. Accordingly, at the end of follow-up, all Group B1 subjects presented clinical remission, while 6 and 12 Group A MTC patients had structural and biochemical persistent disease, respectively. Thank to active surveillance, only 13/63 subjects younger than 18 years at RET screening have been operated on during childhood and/or adolescence. In Group B1, three patients, while actively surveilled, had the possibility to reach the age of 18 (or older) and two patients the age of 15, before being submitted to thyroid surgery. In Group B2, 12 patients become older than 18 years and 17 older than 15 years. In conclusion, we demonstrated that an active surveillance pursuing an early thyroid surgery could be safely recommended in GCs. This patient-centered approach permits postponing thyroid surgery in children until their adolescence/adulthood. At the same time, we confirmed that genetic screening allows finding hidden MTC cases that otherwise would be diagnosed much later.

Higher RET Gene Expression Levels Do Not Represent anAlternative RET Activation Mechanism in Medullary Thyroid Carcinoma

This study was designed to investigate whether RET (rearranged during transfection) mRNA over-expression could be considered an alternative driver event for the development of medullary thyroid carcinoma (MTC), and if different RET isoforms could play a role in MTC tumorigenesis. Eighty-three MTC patients, whose mutational profile was previously identified by next-generation sequencing (NGS) IONS5, were included in this study. Expression analysis was performed by the quantitative reverse transcription-polymerase chain reaction technique. RET expression levels were found to be significantly higher in cases with RET somatic mutations than in cases that were negative for RET somatic mutations (p = 0.003) as well as in cases with a somatic mutation, either in RET or RAS than in cases negative for both these mutations (p = 0.01). All cases were positive for the RET51 isoform expression while only 72/83 (86.7%) were positive for RET9 isoform expression. A statistically significant higher expression of the RET51 isoform was found in cases positive for RET somatic mutation than in cases either positive for RAS mutation (p = 0.0006) or negative for both mutations (p = 0.001). According to our data, RET gene over-expression does not play a role in MTC tumorigenesis, neither as an entire gene or as an isoform. At variance, the RET gene, and in particular the RET51 isoform, is expressed higher in RET mutated cases. On the basis of these results we can hypothesize that the overexpression of RET, and in particular of RET51, could potentiate the transforming activity of mutated RET, making these cases more aggressive.

Whole Tumor Capsule Is Prognostic of Very Good Outcome in the Classical Variant of Papillary Thyroid Cancer

CONTEXT

Tumor capsule integrity is becoming a relevant issue to predict the biological behavior of human tumors, including thyroid cancer.

OBJECTIVE

This work aims to verify whether a whole tumor capsule in the classical variant of papillary thyroid carcinoma (CVPTC) could have as a predictive role of a good outcome as for follicular variant (FVPTC).

METHODS

FVPTC (n = 600) and CVPTC (n = 554) cases were analyzed. We distinguished between encapsulated-FVPTC (E-FVPTC) and encapsulated-CVPTC (E-CVPTC) and, thereafter, invasive (Ei-FVPTC and Ei-CVPTC) and noninvasive (En-FVPTC and En-CVPTC) tumors, according to the invasion or integrity of the tumor capsule, respectively. Cases without a tumor capsule were indicated as invasive-FVPTC (I-FVPTC) and invasive-CVPTC (I-CVPTC). The subgroup of each variant was evaluated for BRAF mutations.

RESULTS

E-FVPTC was more frequent than E-CVPTC (P < .001). No differences were found between En-FVPTC and En-CVPTC or between Ei-FVPTC and Ei-CVPTC. After 18 years of follow-up, a greater number of not-cured cases were observed in Ei-CVPTC with respect to Ei-FVPTC, but not in En-CVPTC to En-FVPTC. Multivariate clustering analysis showed that En-FVPTC, En-CVPTC, and Ei-FVPTC have similar features but different from I-FVPTC and I-CVPTC and, to a lesser extent, from Ei-CVPTC. A total of 177 of 614 (28.8%) cases were BRAFV600E mutated, and 10 of 614 (1.6%) carried BRAF-rare alterations. A significantly higher rate of En-CVPTC (22/49, 44.9%) than En-FVPTC (15/195, 7.7%) (P < .0001) were BRAFV600E mutated.

CONCLUSION

En-CVPTC is less prevalent than En-FVPTC. However, it has good clinical/ pathological behavior comparable to En-FVPTC. This finding confirms the good prognostic role of a whole tumor capsule in CVPTC as well. New nomenclature for En-CVPTC, similar to that introduced for En-FVPTC (ie, noninvasive follicular thyroid neoplasm with papillary-like nuclear features; NIFTP) could be envisaged.

RET mutated C-cells proliferate more rapidly than non-mutated neoplastic cells

A statistically significant higher prevalence of the RET p.Met918Thr somatic mutation, identified by direct sequencing, was previously reported in MTC > 2 cm than in smaller tumors. Aim of this study was to correlate the full RET and RAS mutation profile, identified by a Next Generation Sequencing approach, with the growth rate, proliferation and tumor size of MTC. Data of 149 sporadic MTC patients were correlated with RET mutations and Ki67 positivity. Eighty-one cases had a somatic RET mutation, 40 had a RAS mutation and 28 were negative. A statistically significant higher prevalence of RET mutations was found in MTC > 2 cm. A higher prevalence of RET more aggressive mutations, higher allelic frequencies and, higher percentage of Ki67 positive cells were found in larger tumors which had also a worse outcome. Our study highlights the predominant role of RET somatic mutations in MTC tumorigenesis. We demonstrate that RET mutation prevalence and allelic frequency (AF) are significantly higher in larger tumors. Based on these results, we can conclude that RET mutated C-cells's growth and proliferation are more rapid than those of non-mutated cells and give origin to bigger and more aggressive MTC.

RET Copy Number Alteration in Medullary Thyroid Cancer Is a Rare Event Correlated with RET Somatic Mutations and High Allelic Frequency

Copy number variations (CNV) of the RET gene have been described in 30% of Medullary Thyroid Cancer (MTC), but no information is available about their role in this tumor. This study was designed to clarify RET gene CNV prevalence and their potential role in MTC development. RET gene CNV were analyzed in 158 sporadic MTC cases using the ION Reporter Software (i.e., in silico analysis) while the multiplex ligation-dependent probe amplification assay (i.e., in vitro analysis) technique was performed in 78 MTC cases. We identified three categories of RET ploidy: 137 in 158 (86.7%) cases were diploid and 21 in 158 (13.3%) were aneuploid. Among the aneuploid cases, five out of 21 (23.8%) showed an allelic deletion while 16 out of 21 (76.2%) had an allelic amplification. The prevalence of amplified or deleted RET gene cases (aneuploid) was higher in RET positive tumors. Aneuploid cases also showed a higher allelic frequency of the RET driver mutation. The prevalence of patients with metastatic disease was higher in the group of aneuploid cases while the higher prevalence of disease-free patients was observed in diploid tumors. A statistically significant difference was found when comparing the ploidy status and mortality. RET gene CNVs are rare events in sporadic MTC and are associated with RET somatic mutation, suggesting that they could not be a driver mechanism of tumoral transformation per se. Finally, we found a positive correlation between RET gene CNV and a worse clinical outcome.

MON-524 Prospective Evaluation of Patients with Encapsulated Classical Variant of Papillary Thyroid Cancer and Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features (NIFTP): Have They A Similar Prognosis?

Background: Our previous retrospective study demonstrated that the absence of tumor capsule or, if present, its invasion were independent risk factors for the persistence of the disease (OR 6.75, CI 1.97-23.08 and OR 7.89, CI 1.78-34.94, respectively) in papillary thyroid cancer (PTC). This data was confirmed also analyzing separately the most frequent PTC variants [follicular variant (FVPTC) and classical variant (CVPTC)]. Moreover, we demonstrated that the absence of tumor capsule was significantly more frequent in FVPTC BRAF V600E mutated than FVPTC wild-type for BRAF gene or with rare-BRAF mutations (e.g., BRAF K601E, BRAF V600_K601delinsE). These data confirmed the importance of the integrity of the tumor capsule in FVPTC which led in 2016 to the definition of a new thyroid neoplasm entity named NIFTP. According to these retrospective data, we have assumed that the integrity of the tumor capsule in CVPTC could have a prognostic role similar to that confirmed in the NIFTP group.

Methods: we have prospectively collected data of patients (pts) underwent total thyroidectomy or lobectomy for encapsulated-CVPTC (E-CVPTC) or NIFTP. In both cases the tumor was accurately analyzed by the pathologists according to the criteria used for the NIFTP (in particular with one capsule sample every 1 mm). All pts performed at least one clinical control and neck US within 6 months from surgery.

Results: From January 2018 to June 2019, 144 E-CVPTC and 177 NIFTP were prospectively collected. 83/144 (57.6%) E-CVPTC and 106/177 (59.8%) NIFTP cases were included. The others were excluded due to the presence of other thyroid tumors associated in the same gland. No differences in epidemiological and pathological features were found between E-CVPTC and NIFTP except for the tumor size, significantly bigger in NIFTP than E-CVPTC [22±16mm (2-68) vs 8±11mm (1-80), p<0.00]. A significantly higher rate of NIFTP’ pts underwent lobectomy respect to E-CVPTC pts (34%vs14.5%, p=0.02). After a mean of 9 months of follow-up all pts had an excellent response according to ATA guidelines.

Conclusions: These prospective data demonstrated that NIFTP and E-CVPTC have a similar clinical behavior in a short-term follow-up, thus suggesting that the presence of an intact tumor capsule is predictive of a good outcome. A longer follow up is needed to confirm these initial interesting findings.

MON-490 Calcitonin-Based Thyroidectomy Is a Safe Approach in Patients with Germline RET Mutation and Permits to Delay Surgery in Children

Introduction: Medullary thyroid cancer (MTC) arises from C cells secreting calcitonin. In familial MTC cases, a germline RET mutation is discovered in 98% of cases. Nowadays, an early diagnosis and radical surgery are the only curative approach. However, thyroidectomy in children is associated with a higher rate of surgical adverse events, compared to surgery in adults. The best clinical approach in patient harboring germline RET mutation (gene carriers, GC) is still undefined. Methods and materials: since 1994 to 2018 we identified 174 GC by RET screening. 56 GC underwent total thyroidectomy and lymph node dissection for the evidence of high calcitonin levels at the first clinical evaluation, whereas 27 GC underwent surgery for high stimulated calcitonin levels during the active surveillance (median 16 months, range 13-118). 90 GC are still in follow up. Results: In the group of 27 GC patients who underwent surgery during the active surveillance, 15 GC had only C cells hyperplasia (CCH) foci and 12 were affected by MTC. These carcinomas were all confined to the thyroid, without any lymph node and distant metastasis. All these patients are still in clinical remission, after a median follow-up of 4 years (range 1-11). At time of the surgery, the patients affected by MTC were significantly older than patients harboring only CCH (median 49 vs 30 years old, respectively). Among these 27 GC, 7 were diagnosed as GC when they were younger than 18 years (median 7 years old, range 2-18) and they underwent surgery after a median period of 3 years (range 1-10 years), when they were all older than 7 years. In this group, 6 of 7 were affected by CCH and only one case by a microMTC. There were not any persistent surgical adverse events and all of them are still in clinical remission. 41 of 90 GC, who are still in active surveillance, were younger than 18 years at time of RET screening: nowadays, 10/41 are older than 18 years and 15/41 are older than 14 years, all with calcitonin still in the normal range. Conclusions: we demonstrated that the calcitonin-based thyroidectomy is a safe approach in GC. Intriguingly, this approach seems to be interesting especially in children in order to perform still an early and safe surgery but when they are older, possibly adults.

Medullary thyroid cancer treated with vandetanib: predictors of a longer and durable response

Vandetanib is an important treatment option for advanced metastatic medullary thyroid cancer. The aims of this study were to evaluate the predictors of both a longer response to vandetanib and the outcome. Medical records of 79 medullary thyroid cancer patients treated with vandetanib at our center were analysed. Twenty-five patients were treated for <12 months, 54 were treated for ≥12 months and 24 of these latter were treated for ≥48 months (short-, long- and very long-term). The median progression free survival of the long and very long-term treated patients was significantly longer than in the ZETA trial. When comparing the groups of short - and long-term treated patients the only significant difference was that these latter were less frequently previously treated with a tyrosine kinase inhibitor. However, the long-term treated patients had a younger age, both at diagnosis and enrolment, which was statistically significant in the very long-term treated patients. In the long-term treated group, younger age, enrolment for symptoms and development of adverse events were significantly correlated with a better outcome. The enrolment for symptoms remained the only statistically significant predictor of a good outcome in the very long-term treated patients. In conclusion, early treatment with vandetanib, when patients are younger, with a good ECOG performance status and symptomatic disease, not necessarily progressing for RECIST, seem to be the best predictors of a longer and durable response. Further studies are needed to confirm these results

Genetic Landscape of Somatic Mutations in a Large Cohort of Sporadic Medullary Thyroid Carcinomas Studied by Next-Generation Targeted Sequencing

Sporadic Medullary Thyroid Carcinoma (sMTC) is a rare but aggressive thyroid tumor. RET and RAS genes are present in about 50%-80% of cases, but most of the remaining cases are still orphan of a genetic driver. We studied the largest series of sMTC by deep sequencing to define the mutational landscape. With this methodology we greatly reduced the number of RET- or RAS-negative cases and we confirmed the central role of RET and RAS mutations. Moreover, we highlighted the bad prognostic role of RET mutations in sMTC and consolidated the favorable prognostic role of RAS mutations. For the first time, we showed that the variant allele frequency represents an additional prognostic marker inside the group of RET-mutated sMTC.

Differential expression of RET isoforms in normal thyroid tissues, papillary and medullary thyroid carcinomas

POURPOSES

We investigated the expression of RET9 and RET51 isoforms in medullary (MTC), papillary (PTC) thyroid carcinoma, normal thyroid tissues, and pheochromocytoma (PHEO) to verify if these isoforms are present also in follicular thyroid cell-derived tissues, and if there is a differential expression of RET9 and RET51 in MTC.

METHODS

Nineteen patients with MTC, 18 patients with PTC, 18 samples of contralateral normal thyroid tissues, and 5 cases of PHEO were included in this study. RET isoform expression was studied by real-time RT-PCR.

RESULTS

All MTCs and PHEOs were positive for RET9 and RET51. Fourteen/eighteen (77.7%) PTC cases were positive for RET9 and/or RET51, and four were positive for only one of the genes. In normal thyroid tissues, 3/18 (16.7%) cases were negative for both isoforms, 4/18 (22.2%) were positive for both, and 11/18 (61.1%) were positive for only one. RET isoforms were expressed at different levels in MTC, PHEO, PTC, and normal thyroid tissues: RET9 expression was higher in PHEO than in MTC, PTC, and normal thyroid tissues. RET9 expression was also higher in MTC than in PTC and normal thyroid tissues. No difference was observed between PTC and normal thyroid tissues. A similar pattern of expression was observed for RET51. In addition, RET51 was significantly more expressed than RET9 in MTC, while RET9 was the predominant isoform in PHEO.

CONCLUSIONS

Our study documented the expression of the RET9 and RET51 isoforms in normal thyroid and PTC tissues. RET9 and RET51 isoforms were also present in MTC and PHEO. RET51 expression was higher than RET9 expression in MTC, while there was no difference in the expression of these two isoforms in PTC and normal thyroid tissues. RET9 was more highly expressed than RET51 in PHEOs.

Lung Recurrence of Papillary Thyroid Cancer Diagnosed With Antithyroglobulin Antibodies After 10 Years From Initial Treatment

Introduction: Papillary thyroid cancer (PTC) is the most common endocrine malignancy. More than 98% of patients achieve an excellent response with no evidence of clinical, biochemical, or structural disease after initial treatment. In these patients structural recurrence is rare, more frequently diagnosed in the first 5 years from initial treatment and almost invariably localized in neck lymph nodes. Patient: We report the case of a woman affected by PTC who presented with rapidly rising anti-thyroglobulin antibodies (TgAb) level after 10 years from clinical, morphological and biochemical remission. Diagnosis and Treatment: In 2003, a 56 year old patient was treated with total thyroidectomy and radioiodine remnant ablation (RRA) for a PTC (2 cm) with minimal extrathyroidal extension (T3N1aM0 according to the 6th AJCC TNM staging system) associated with diffuse lymphocytic thyroiditis. In 2004 the patient was free of disease defined as undetectable Tg after recombinant human TSH administration in the absence of TgAb and structural disease. Since February 2012 the appearance and progressive increase of TgAb titer was observed and in 2014 a ¹⁸FDG-PET scan documented three hypermetabolic lesions suggestive of lung micrometastases. The lung lesions were cytologically confirmed as PTC metastases. Both the primary tissue and the lung metastasis were positive for BRAF V600E mutation. The patient was treated with 131-radioiodine that showed radioiodine avid lung lesions that lose the ability to take up iodine at the following treatment. The patient is still alive and the lung lesions are growing slowly. Conclusions: Structural recurrence in patients that demonstrated an excellent response after initial treatment for PTC is extremely rare, and distant metastases exceptional but possible. This case is peculiar because recurrence was early identified after 10 years from initial treatment for the presence of detectable TgAb in a patient that had an histological diagnosis of lymphocytic thyroiditis but with an atypical clinical presentation (normal thyroid at neck ultrasound and undetectable TgAb and anti-thyroid peroxidase antibodies). For this reason TgAb should be tested with Tg in patients with a history of lymphocytic thyroiditis, either histological or humoral, also when TgAb is in the normal range and not suggestive of autoimmune thyroiditis.