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Simple Summary: Since the discovery of the RET gene in the early 1980s, multiple treatments have been developed that can inhibit abnormal RET signaling. The first treatments were repurposed multikinase inhibitors, however, their low selectivity for RET led to unacceptable off-target toxicities and sub-optimal exposure in patients. More RET-specific or selective RET inhibitors (SRIs; selpercatinib and pralsetinib) were developed and were subsequently approved and are now established as standard of care treatment across a variety of indications including lung and thyroid cancer. However, there is now a need to develop treatment strategies that can address acquired resistance to these agents, including the development of next-generation SRIs and novel combination approaches. There also remains an opportunity to improve on the efficacy and safety/tolerability profile of the currently approved SRIs, especially to support potential combination approaches. This review discusses the current treatment landscape for RET-altered tumors and progress in the development of the next generation of SRIs. RET is a receptor tyrosine kinase that plays an important role in the development of neurons and kidneys. The gene encoding the rearranged-during-transfection (RET) receptor tyrosine kinase was first discovered in the 1980s. Activating RET mutations and rearrangements have since been identified as actionable drivers of oncogenesis in numerous cancer types and are most prevalent in thyroid and non-small-cell lung cancer. Following the modest success of repurposed RET-active multikinase inhibitors, the first selective RET inhibitors (SRIs), selpercatinib and pralsetinib, received regulatory approval in 2020. Now, thousands of patients with RET-altered cancers have benefited from first-generation SRIs, with impressive deep and durable responses. However, following prolonged treatment with these SRIs, a number of acquired on-target resistance mutations have been identified together with other non-RET-dependent resistance mechanisms. Today, the focus is on how we can further evolve and improve the treatment of RET-altered tumors with next-generation SRIs, and a number of candidate drugs are in development. The ideal next-generation SRIs will be active against on-target acquired resistance alterations, including those that emerge in the CNS, and will have improved safety and tolerability relative to first-generation SRIs. In this review, we will provide an update on these candidates and their potential to meet the unmet clinical need for patients who progress on first-generation SRIs. [ABSTRACT FROM AUTHOR]

Aggressiveness and age of manifestation of medullary thyroid cancer depend on the risk level of germline RET mutations. For high-risk mutations, preventive thyroidectomy is recommended at young age. In recent years, endoscopic operations for thyroid cancer were introduced in clinical practice. But such experience in pediatrics is very limited. We present a case report of a male patient, 6-year-old with the high-risk germline mutation С634R in RET gene. Close relatives (mother, cousin, and native sister) of the proband, were treated for medullary thyroid cancer. Also, his grandmother on the maternal line and her native brother died at the age of 38 and 37 years because of medullary thyroid cancer progression. Since 3 years old, our patient was under regular exams. At the age of six, calcitonin level was 8 ng/mL, and no evidence of pathology on ultrasound. According to recommendations of American Thyroid Association from 2015 (ATA 2015), preventive thyroidectomy was planned. This operation was performed by transoral vestibular approach. Oral nutrition started on the first day after the operation and the patient was discharged from the hospital. No major complications were observed. Transitory paresthesia and slight edema of the submental compartment were noticed. Consider this, endoscopic operation on the thyroid gland can be performed, as a preventive procedure, for RET gene germline mutation carriers in young age. This method helps avoid scars on the skin of the anterior neck.

Opinion statement: Genetic assessment is crucial to address the correct treatment for advanced medullary thyroid cancer (MTC). Multi tyrosine kinase inhibitors (mTKIs) cabozantinib and vandetanib are good first line options, even vandetanib prescription is currently limited to RET mutated patients. Selective RET inhibitors such as pralsetinib could be a preferred upfront treatment in case of RET mutated MTC presenting common or gatekeeper RET mutations (e.g. M918T; V804L/M). Selpercatinib, otherwise, can be prescribed as the second line after disease progression to mTKIs. The best option for subsequent lines is to consider inclusion in clinical trials or alternatively other mTKIs such as sunitinib, sorafenib, lenvatinib, or pazopanib could be evaluated. New perspectives include next-generation RET inhibitors able to overcome resistance mechanisms responsible for disease progression to standard mTKIs and RET inhibitors, and immunotherapy for MTC presenting with high tumor mutational burden. [ABSTRACT FROM AUTHOR]

Objective: To determine genealogical, clinical and pathological characteristics of a cohort with Cys618Arg mutation from an Israeli multicenter MTC study. Methods: Retrospective database analysis examining RET mutations and comparing Cys618Arg and Cys634Arg/Thr/Tyr subgroups. Results: Genetic testing was performed in 131/275 MTC patients (47.6%). RET mutations were found in 50/131 (38.2%), including Cys618Arg (28/50 cases, 56%), and Cys634Arg/Thr/Tyr (15/50,30%). Through genealogical study, 31 MTC patients were found descendants of one family of Jewish Moroccan descent, accounting for 27/28 patients with documented Cys618Arg mutation and 4 patients without available genetic testing. Familial Cys618Arg cases (n=31) and Cys634Arg/Thr/Tyr cases (n=15, from 6 families) were compared. Although surgical age was similar (25.7 vs 31.3 years, p=0.19), the Cys618Arg group had smaller tumors (8.9mm vs 18.5mm, p=0.004) and lower calcitonin levels (33.9 vs 84.5 X/ULN, p=0.03). Youngest ages at MTC diagnosis were 8 and 3 years in Cys618Arg and Cys634Arg/Thr/Tyr cohorts, respectively. Long-term outcome was similar between groups. The Cys618Arg cohort had lower rates of pheochromocytoma (6.5% vs 53.3%, p=0.001) and primary hyperparathyroidism (3.2% vs 33.3%, p=0.01). Conclusion: This is the first description of RET mutation distribution in Israel. Of 131 tested MTC patients, Cys618Arg was the predominant mutation. To the best of our knowledge, this is the largest cohort of Cys618Arg mutation described. For Cys618Arg and Cys634Arg/Thr/Tyr cohorts, MTC was diagnosed earlier than expected, likely due to familial genetic screening, and MTC outcomes were similar between groups. International studies are necessary to further characterize the clinical features of Cys618 mutations due to their relative rarity. [ABSTRACT FROM AUTHOR]

ObjectiveTo determine genealogical, clinical and pathological characteristics of a cohort with Cys618Arg mutation from an Israeli multicenter MTC study.MethodsRetrospective database analysis examining RET mutations and comparing Cys618Arg and Cys634Arg/Thr/Tyr subgroups.ResultsGenetic testing was performed in 131/275 MTC patients (47.6%). RET mutations were found in 50/131 (38.2%), including Cys618Arg (28/50 cases,56%), and Cys634Arg/Thr/Tyr (15/50,30%). Through genealogical study, 31 MTC patients were found descendants of one family of Jewish Moroccan descent, accounting for 27/28 patients with documented Cys618Arg mutation and 4 patients without available genetic testing. Familial Cys618Arg cases (n=31) and Cys634Arg/Thr/Tyr cases (n=15, from 6 families) were compared. Although surgical age was similar (25.7 vs 31.3 years, p=0.19), the Cys618Arg group had smaller tumors (8.9mm vs 18.5mm, p=0.004) and lower calcitonin levels (33.9 vs 84.5 X/ULN, p=0.03). Youngest ages at MTC diagnosis were 8 and 3 years in Cys618Arg and Cys634Arg/Thr/Tyr cohorts, respectively. Long-term outcome was similar between groups. The Cys618Arg cohort had lower rates of pheochromocytoma (6.5% vs 53.3%, p=0.001) and primary hyperparathyroidism (3.2% vs 33.3%, p=0.01).ConclusionThis is the first description of RET mutation distribution in Israel. Of 131 tested MTC patients, Cys618Arg was the predominant mutation. To the best of our knowledge, this is the largest cohort of Cys618Arg mutation described. For Cys618Arg and Cys634Arg/Thr/Tyr cohorts, MTC was diagnosed earlier than expected, likely due to familial genetic screening, and MTC outcomes were similar between groups. International studies are necessary to further characterize the clinical features of Cys618 mutations due to their relative rarity.

Aggressiveness and age of manifestation of medullary thyroid cancer depend on the risk level of germline RET mutations. For high-risk mutations, preventive thyroidectomy is recommended at young age. In recent years, endoscopic operations for thyroid cancer were introduced in clinical practice. But such experience in pediatrics is very limited. We present a case report of a male patient, 6-year-old with the high-risk germline mutation С634R in RET gene. Close relatives (mother, cousin, and native sister) of the proband, were treated for medullary thyroid cancer. Also, his grandmother on the maternal line and her native brother died at the age of 38 and 37 years because of medullary thyroid cancer progression. Since 3 years old, our patient was under regular exams. At the age of six, calcitonin level was 8 ng/mL, and no evidence of pathology on ultrasound. According to recommendations of American Thyroid Association from 2015 (ATA 2015), preventive thyroidectomy was planned. This operation was performed by transoral vestibular approach. Oral nutrition started on the first day after the operation and the patient was discharged from the hospital. No major complications were observed. Transitory paresthesia and slight edema of the submental compartment were noticed. Consider this, endoscopic operation on the thyroid gland can be performed, as a preventive procedure, for RET gene germline mutation carriers in young age. This method helps avoid scars on the skin of the anterior neck. [ABSTRACT FROM AUTHOR]

Simple Summary: Approximately 20% of medullary thyroid cancers (MTC) are hereditary and caused by specific germline RET protooncogene mutations. Screening for germline mutation in all newly identified cases and their relatives allows early or even prophylactic surgical treatment. The aim of this retrospective study was to assess the clinical features of RET mutation carriers according to the age at surgery and the long-term outcome in term of morbidity and recurrence rate after prophylactic and early thyroidectomy. The results demonstrated that prophylactic and early thyroidectomy are safe and effective procedures in achieving the cure; however, while patients with only C-cell hyperplasia are disease-free, patients with MTC, even when small and confined to the gland, could have recurrent disease at long-term. This finding suggest that prophylactic surgery should be performed earlier. Prophylactic and early thyroidectomy in RET germline mutation carriers allows the removal of the thyroid before medullary thyroid carcinoma (MTC) develops, or while it is still confined to the gland. This study was aimed to assess the clinicopathological features in RET carriers according to the age at surgery and the long-term outcomes after prophylactic and early thyroidectomy. A retrospective analysis of 63 operated asymptomatic RET carriers diagnosed after familial genetic screening was performed. Twenty-one RET carriers were operated at pediatric (<18 yrs) and 42 at adult (≥18 yrs) age. Serum preoperative calcitonin levels were significantly lower in pediatric compared to adult patients (p = 0.04); moreover, adult RET carriers had a greater frequency of microMTC at pathology (p = 0.009). Permanent postoperative morbidity occurred in 9.5% of patients, without differences between the two groups. Biochemical postoperative cure was achieved in all patients. At a median follow-up of 14 years, all C-cell hyperplasia patients are disease-free; conversely, biochemical, and structural recurrence of disease occurred in three adults and one pediatric patient with microMTC. The independent predictive factors of MTC were the age at surgery, the preoperative calcitonin level and the RET mutational risk profile (p < 0.02). In conclusion, prophylactic and early thyroidectomy are safe and effective procedures in achieving definitive cure in most RET carriers. However, since recurrences may occur at long-term in case of microMTC, thyroidectomy should be possibly performed earlier to prevent microMTC development. [ABSTRACT FROM AUTHOR]

RET is a receptor tyrosine kinase that plays an important role in the development of neurons and kidneys. The gene encoding the rearranged-during-transfection ( RET ) receptor tyrosine kinase was first discovered in the 1980s. Activating RET mutations and rearrangements have since been identified as actionable drivers of oncogenesis in numerous cancer types and are most prevalent in thyroid and non-small-cell lung cancer. Following the modest success of repurposed RET-active multikinase inhibitors, the first selective RET inhibitors (SRIs), selpercatinib and pralsetinib, received regulatory approval in 2020. Now, thousands of patients with RET-altered cancers have benefited from first-generation SRIs, with impressive deep and durable responses. However, following prolonged treatment with these SRIs, a number of acquired on-target resistance mutations have been identified together with other non-RET-dependent resistance mechanisms. Today, the focus is on how we can further evolve and improve the treatment of RET-altered tumors with next-generation SRIs, and a number of candidate drugs are in development. The ideal next-generation SRIs will be active against on-target acquired resistance alterations, including those that emerge in the CNS, and will have improved safety and tolerability relative to first-generation SRIs. In this review, we will provide an update on these candidates and their potential to meet the unmet clinical need for patients who progress on first-generation SRIs.

Inherited mutations in the RET proto-oncogene, which encodes a receptor tyrosine kinase, predispose individuals to the multiple endocrine neoplasia type 2 (MEN 2) cancer syndromes. The major component tumor of these syndromes is medullary thyroid carcinoma (MTC). To date, somatic mutations in RET have been identified in tumors from individuals with MEN 2 finding. RET M918T mutation is present in 95 % of the MEN2B cases, and approximately 50 % of sporadic MTCs harbor this mutation. We performed a mutational analysis in 17 cases of Medullary thyroid carcinoma, the somatic missense mutation at codon 918 of RET was found in 2 of the 17 MTCs, and one case presented MEN2 phenotype including MTC. The percentage of RET M918T mutation is similar in Mexican MTC patients to other series, although other mutations could be implicated in our population. [ABSTRACT FROM AUTHOR]

Although rare, medullary thyroid cancer (MTC) exemplifies the value that ever-expanding knowledge of molecular pathways and mechanisms brings to managing challenging cancers. Although surgery can be curative for MTC in many patients, a substantial proportion of patients present with locoregional or distant metastatic disease. Once distant disease occurs, treatment options are limited, and conventional cancer treatments such as cytotoxic chemotherapy are of minimal benefit. Biomarkers such as calcitonin and carcinoembryonic antigen are important correlates of disease burden as well as predictors of disease progress, including recurrence and survival. MTC is either sporadic (∼75%) or inherited (∼25%) as an autosomal dominant disease. Regardless, germline and somatic mutations, particularly in the rearranged during transfection (RET) proto-oncogene, are key factors in the neoplastic process. Gain-of-function RET mutations result in overactive proteins that lead to abnormal activation of downstream signal transduction pathways, resulting in ligand-independent growth and resistance to apoptotic stimuli. Specific RET mutation variants have been found to correlate with phenotype and natural history of MTC with some defects portending a more aggressive clinical course. Greater understanding of the consequence of the aberrant signaling pathway has fostered the development of targeted therapies. Two small-molecule tyrosine kinase inhibitors, vandetanib and cabozantinib, are currently available as approved agents for the treatment of advanced or progressive MTC and provide significant increases in progression-free survival. Since there have been no head-to-head comparisons, clinicians often select between these agents on the basis of familiarity, patient characteristics, comorbidities, and toxicity profile. [ABSTRACT FROM AUTHOR]

Advanced medullary thyroid cancers (MTCs) are now being treated with drugs that inhibit receptor tyrosine kinases, many of which involved in angiogenesis. Response rates vary widely, and toxic effects are common, so treatment should be reserved for MTCs likely to be responsive to these drugs. RET mutations are common in MTCs, but it is unclear how they influence the microvascularization of these tumors. We examined 45 MTCs with germ-line or somatic RET mutations (RETmut group) and 34 with wildtype RET (RETwt). Taqman Low-Density Arrays were used to assess proangiogenic gene expression. Immunohistochemistry was used to assess intratumoral, peritumoral and nontumoral expression levels of VEGFR1, R2, R3, PDGFRa, PDGFB and NOTCH3. We also assessed microvessel density (MVD) and lymphatic vessel density (LVD) based on CD31-positive and podoplanin-positive vessel counts, respectively, and vascular pericyte density based on staining for a-smooth muscle actin (a-SMA), a pericyte marker. Compared with RETwt tumors, RETmut tumors exhibited upregulated expression of proangiogenic genes (mRNA and protein), especially VEGFR1, PDGFB and NOTCH3. MVDs and LVDs were similar in the two groups. However, microvessels in RETmut tumors were more likely to be a-SMA positive, indicating enhanced coverage by pericytes, which play key roles in vessel sprouting, maturation and stabilization. These data suggest that angiogenesis in RETmut MTCs may be more intense and complete than that found in RETwt tumors, a feature that might increase their susceptibility to antiangiogenic therapy. Given their increased vascular pericyte density, RETmut MTCs might also benefit from combined or preliminary treatment with PDGF inhibitors. [ABSTRACT FROM AUTHOR]

Medullary thyroid carcinomas (MTCs) are rare neoplasms comprising 2-10% of all thyroid malignancies. More than 75% are sporadic tumors and the remainder is familial and MEN2 related. Both sporadic and syndromic MTCs frequently show mutations in the RET proto-oncogene. It has been noted that some MTC cases present an indolent, and some an aggressive clinical course. Ki-67 expression is generally low, with documented exceptions, whereas high expression of Bcl-2 has been reported in majority of the cases. Some studies have shown that Ki-67 and Bcl-2 expressions have prognostic value, as well as RET mutational status. We analyzed 20 unrelated MTC cases for Ki-67, Bcl-2 expression and RET mutations and tested their intercorrelations, correlations to the morphologic features and stage of the tumors, as well as their influence on survival. In 13 of the 20 analyzed cases we found 23 sequence changes distributed in exons 8, 10-13 and 16. There were 11 different missense mutations, single nucleotide deletion with frameshift, and 8 different synonymous mutations. Only 4 of the sequence changes have been previously published. Twelve patients (60%) had tumors expressing one or more missense mutations or single nucleotide deletion and 7 of them (35%) had at least one damaging or possibly damaging RET mutation. Most of the tumors had low Ki-67 expression (mean 6.48% of cells) and high Bcl-2 expression (mean 68.3%). Significantly better survival was observed in cases with low Ki-67 (< 6.5%; p < 0.05), high Bcl-2 expression (> 68.3%; p < 0.01) and younger age at diagnosis (< 51 years; p < 0.05). [ABSTRACT FROM AUTHOR]

Thyroid cancer is an uncommon childhood malignancy that presents primarily in young children or adolescent females and may be related to radiation exposure or genetic predisposition. Gene alterations, such as RET mutation or RET/PTC rearrangement, are not uncommon. Recent studies have lead to an increased understanding of the role of these particular gene alterations in the diagnosis, prognosis, and treatment of thyroid cancer. Surgery remains the mainstay of treatment for thyroid cancer followed by radioactive iodine when appropriate. In patients with MEN2, prophylactic thyroidectomy is recommended, although a delay in the initial diagnosis is common. With early aggressive treatment and long-term follow-up, these patients generally have excellent outcomes. Recent research suggests potential usefulness of novel therapies directed at oncogenic signaling pathways, modulators of growth, angiogenesis inhibitors, immunomodulators, and gene therapy. [ABSTRACT FROM AUTHOR]

Romeo G, Ceccherini I, Celli J, Priolo M, Betsos N, Bonardi G, Seri M, Yin L, Lerone M, Jasonni V, Martucciello G (University of Genoa Medical School, Genoa, Italy; International Agency for Research on Cancer, Lyon, France). Association of multiple endocrine neoplasia type 2 and Hirschsprung disease (Minisymposium: MEN & VHL). J Intern Med 1998; 243: 515–20. In a few patients with Hirschsprung disease (HSCR) and no clinical symptoms of multiple endocrine neoplasia type 2 (MEN-2A) or medullary thyroid carcinoma (MTC), missense mutations in the cysteine residues 609 and 620 of the Ret gene have been identified. In several pedigrees with either MEN-2A or familial MTC (FMTC) a documented germline mutation in cysteine 618 or 620 follows the segregation of the disease phenotype. The appearance of the HSCR phenotype in such patients and pedigrees cannot be easily reconciled with the gain of function which is associated with the dominant oncogenic effect of MEN-2A mutations. Gastrointestinal manifestations are known to occur also in association with MEN-2B but, to the best of our knowledge, in only very few cases the intestinal phenotype of MEN-2B has been investigated by enzymo-histochemical techniques, as in the present work. We report an extensive molecular study of patients, two with HSCR and FMTC carrying a Cys620Arg or Ser mutation and two with MEN-2B and gastrointestinal symptoms carrying a Met918Thr mutation. One of the latter two patients showed aganglionosis of the last 5 cm of rectum which caused a congenital megacolon leading to the diagnosis and operation for HSCR. The mutation screening of all the exons of Ret in 3 of these patients did not reveal any additional mutation. Therefore these results do not support the hypothesis of additional constitutional Ret mutations in patients showing association of MEN-2 and HSCR, whilst the histochemical and clinical data in one of these patients indicate that MEN-2B can be associated with a true form of short segment HSCR. [ABSTRACT FROM AUTHOR]

Simple Summary: The use of novel therapeutic drugs in lung cancer has changed the paradigm of the diagnosis and treatment of lung cancer. Due to the development of advanced diagnostic procedures (e.g., next generation sequencing (NGS)) around half of non-small-cell lung cancer (NSCLC) patients can be identified with genetic aberrations. The presence of activating mutations of EGFR, ALK and ROS-1 have already been well explored. New targets that can be successfully targeted include NTRK, MET, RET and HER 2 genes. Some particles have already received FDA approval, whereas many more are in the late stages of clinical trials. Considering rapid changes in thoracic oncology, an up-to-date summary is needed. In this review, we present the current landscape of approved therapeutic drugs, as well as important ongoing clinical trials. Lung cancer is the most common cause of cancer-related death worldwide, and the prognosis for stage IV remains poor. The presence of genetic alterations in tumor cells, such as EGFR and BRAF gene mutations, as well as ALK and ROS1 gene rearrangements, are indications for targeted therapies. Many such treatments are already registered and used on a wide scale. In comparison to standard chemotherapy, they can prolong not only progression-free survival but also overall survival. Moreover, they are able to provide excellent quality of life and rapid improvement of cancer-related symptoms such as dyspnea, cough and pain. Recent years have witnessed great advances in both molecular diagnostics and new molecular therapies for non-small-cell lung cancer. This review presents new therapeutic targets in NSCLC, as well as drugs of which the activity against NTRK, RET, MET or HER2 gene alterations (including EGFR exon 20 insertions) has either been confirmed or is currently being evaluated. Although these particular genetic alterations in NSCLC are generally rare, each accounting for 1–2% of patients, in total about half of all patients have molecular alterations and may ultimately receive targeted therapies. [ABSTRACT FROM AUTHOR]

Medullary thyroid carcinoma (MTC) still remains a rare endocrine tumor. 20-25% of MTC cases are genetically determined. The detection of the RET proto-oncogene mutation in 1993 allowed to understand the unique genotype-phenotype relationships in hereditary medullary thyroid carcinoma (HMTC) and formed the basis for therapeutic decisions based on the molecular results. Currently, prophylactic thyroidectomy is a commonly adopted and accepted therapeutic method. The decision on the time and extent of surgery should be made based on the results of molecular examination, the assessment of calcitonin (Ct) concentration and family history. Treatment of patients with HMTC requires the cooperation of a multidisciplinary team of experts and should be done in specialized centers only. The study is a review of the current guidelines for surgical management in the MEN2 syndrome.