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Activating receptor-tyrosine kinase rearranged during transfection (RET) mutations and fusions are potent drivers of oncogenesis. The recent FDA approvals of highly potent and selective RET inhibitors, selpercatinib and pralsetinib, has altered the therapeutic management of RET aberrant tumors. There is ample evidence of the role of RET signaling in certain cancers. RET aberrations as fusions or mutations occur in multiple cancers, however, there is considerable phenotypic diversity. There is emerging data on the lack of responsiveness of immunotherapy in RET-altered cancers. Herein, we review the registrational data from the selective RET-inhibitor trials, and comprehensively explore RET alterations in pan-cancer adult malignancies and their co-alterations. These co-occuring alterations may define the future of RET inhibition from specific selective targeting to customized combination therapies as data are rapidly emerging on both on-target and off-target acquired resistance mechanisms. Fascinatingly, oncogenic RET fusions have been reported to mediate resistance to EGFR inhibition and KRASG12C inhibition.

Medullary thyroid cancer (MTC) is an infrequent neuroendocrine tumor, which amounts to 3–5% of all thyroid malignancies. Approximately 75–80% of MTCs are sporadic neoplasms. The rest of 20–25% are familial cases that belong to multiple endocrine neoplasia (MEN) syndromes, specifically MEN2 and MEN3. These cases of familial MTC are attributed to an activating germline mutation of a tyrosine kinase receptor gene, the rearranged during transfection (RET) proto-oncogene, located on chromosome 10q11.21. These mutations are also found in some cases of sporadic MTC. This review sets forth in summary the accepted guidelines and approaches regarding diagnosis, management, and treatment of MTC. Surgical resection is the standard care, and an early, prophylactic intervention is performed in genetic cases. Further investigation and understanding of the molecular pathways involved in the growth and advancement of MTC is required in order to provide efficient therapy in cases of progressive disease.

A novel, specific and precise RP-HPLC method has been developed and validated for the quantification of selpercatinib in pure and its pharmaceutical dosage form. Selpercatinib is a kinase interrupter with increased selectivity for rearranged during transfection (RET) tyrosine kinase receptors (RTKs) above the additional RTK classes. It is used for the treatment of RET fusion-positive non-small cell lung carcinoma (NSCLC). The segregation was accomplished on the Zorbax C18 column (150 x 4.6 mm) with a 5 µ particle size. 0.1% orthophosphoric acid and Acetonitrile (ACN) (60:40 v/v) was used as an optimized mobile phase at a flow rate of 1ml/min. The wavelength selected was 220.0nm. The retention time for selpercatinib was 2.653 min. The linearity of selpercatinib was detected to be 5- 30μg/ml. Linearity equations obtained for selpercatinib was y = 18428x + 2196.2 with correlation coefficient 0.999. The % RSD for precision was found to be less than 2%. %Recovery was obtained as 99.74% for selpercatinib. The LOD and LOQ for selpercatinib were obtained as 0.02 µg/ml and 0.05 µg/ml.

Background: Previous studies have suggested a close association between REarranged during Transfection (RET) c.73 + 9277T > C and c.135G > A polymorphisms and Hirschsprung disease (HSCR) susceptibi...

The rearranged during transfection (RET) gene encodes a protein tyrosine kinase. RET alterations by point mutations and gene fusions were found in diverse cancers. RET fusions allow abnormal expression and activation of the oncogenic kinase, whereas only a few of RET point mutations found in human cancers are known oncogenic drivers. Earlier studies of RET-targeted therapy utilized multi-targeted protein tyrosine kinase inhibitors (TKIs) with RET inhibitor activity. These multi-targeted TKIs often led to high-grade adverse events and were subject to resistance caused by the gatekeeper mutations. Recently, two potent and selective RET TKIs, pralsetinib (BLU-667) and selpercatinib (LOXO-292), were developed. High response rates to these selective RET inhibitors across multiple forms of RET alterations in different types of cancers were observed in clinical trials, demonstrating the RET dependence in human cancers harboring these RET lesions. Pralsetinib and selpercatinib were effective in inhibiting RET

In a healthy adult brain, glial cell line-derived neurotrophic factor (GDNF) is exclusively expressed by neurons, and, in some instances, it has also been shown to derive from a single neuronal subpopulation. Secreted GDNF acts in a paracrine fashion by forming a complex with the GDNF family receptor α1 (GFRα1), which is mainly expressed by neurons and can act in cis as a membrane-bound factor or in trans as a soluble factor. The GDNF/GFRα1 complex signals through interactions with the “rearranged during transfection” (RET) receptor or via the neural cell adhesion molecule (NCAM) with a lower affinity. GDNF can also signal independently from GFRα1 by interacting with syndecan-3. RET, which is expressed by neurons involved in several pathways (nigro−striatal dopaminergic neurons, motor neurons, enteric neurons, sensory neurons, etc.), could be the main determinant of the specificity of GDNF’s pro-survival effect. In an injured brain, de novo expression of GDNF occurs in glial cells. Neuroinflammation has been reported to induce GDNF expression in activated astrocytes and microglia, infiltrating macrophages, nestin-positive reactive astrocytes, and neuron/glia (NG2) positive microglia-like cells. This disease-related GDNF overexpression can be either beneficial or detrimental depending on the localization in the brain and the level and duration of glial cell activation. Some reports also describe the upregulation of RET and GFRα1 in glial cells, suggesting that GDNF could modulate neuroinflammation.

3008 Background: RET (REarranged during Transfection) gene alterations (mutations and fusions) leading to constitutive kinase activity are identified as drivers of disease progression in multiple tumor types, including non-small cell lung cancer (NSCLC) and medullary thyroid cancer (MTC). BOS172738 is an investigational, potent, selective oral RET kinase inhibitor. This next-generation inhibitor was designed with nanomolar potency against RET and >300-fold selectivity against vascular endothelial growth factor receptor 2, to maximize the potential therapeutic window. Methods: NCT03780517 is a phase 1 study consisting of a dose-escalation and dose-expansion phase. During the escalation, 67 patients with RET-altered advanced solid tumors received once-daily oral doses of BOS172738 (10-150 mg). Intra-patient dose escalation was allowed as was over-accrual to dose levels deemed to be safe. Study endpoints were safety (CTCAE v. 4.03), tolerability and confirmed overall response rate (ORR; RECIST 1.1). The data cutoff was Dec. 11, 2020. Results: BOS172738 exhibited a favorable safety profile (n=67) for long-term administration with most treatment-emergent adverse events (TEAEs) classified as grade ≤2 and deemed unrelated to drug. The most common TEAEs were creatinine phosphokinase (CPK) increase (54%), dyspnea (34%), facial edema, aspartate aminotransferase elevation, anemia (25% each), neutropenia, diarrhea (22% each), fatigue (21%), and constipation (20%). BOS172738 was not associated with hypertension or significant hepatoxicity. BOS172738 demonstrated broad anti-tumor activity with an investigator-assessed ORR of 33% (n=18/54), a NSCLC ORR of 33% (n=10/30), MTC ORR of 44% (n=7/16, including 1 complete response) and one patient with RET fusion+ pancreatic cancer reported a partial response. Responders included patients with brain metastases with one patient whose brain lesion decreased by 43%. The median duration of response has not been reached. Many patients remain on study, including the longest of 659 days, at data cutoff. BOS172738 exhibited dose-dependent exposure (AUC, Cmax), rapid absorption (median Tmax 1 to 4.5 h), and an extended half-life (approximately 65 hours) maximizing target coverage. Conclusions: BOS172738 is a highly potent and selective RET inhibitor with a differentiated safety profile and clinical activity against RET-altered tumors, including patients with brain metastases. BOS172738 continues to be evaluated in patients with NSCLC, MTC, and in patients previously treated with other selective RET inhibitors. Clinical trial information: NCT03780517.

Introduction: Rearranged during transfection (RET) gene fusions are rare genetic drivers in non-small cell lung cancer (NSCLC). Selective RET-inhibitors such as selpercatinib have shown therapeutic activity in early clinical trials; however, their efficacy in the real-world setting is unknown. Methods: A retrospective efficacy and safety analysis was performed on data from RET fusion-positive NSCLC patients who participated in a selpercatinib access program (named patient protocol) between August 2019 and January 2021. Results: Data from 50 patients with RET fusion-positive advanced NSCLC treated with selpercatinib at 27 centers in 12 countries was analyzed. Most patients were Non-Asian (90%), female (60%), never-smokers (74%), with a median age of 65 years (range, 38–89). 32% of the patients had known brain metastasis at the time of selpercatinib treatment. Overall, 13 patients were treatment-naïve, while 37 were pretreated with a median of three lines of therapy (range, 1–8). The objective response rate (ORR) was 68% [95% confidence interval (CI), 53–81] in the overall population. The disease control rate was 92%. The median progression-free survival was 15.6 months (95% CI, 8.8–22.4) after a median follow-up of 9 months. In patients with measurable brain metastases ( n = 8) intracranial ORR reached 100%. In total, 88% of patients experienced treatment-related adverse events (TRAEs), a large majority of them being grade 1 or 2. The most common grade ⩾ 3 TRAEs were increased liver enzyme levels (in 10% of patients), prolonged QTc time (4%), abdominal pain (4%), hypertension (4%), and fatigue/asthenia (4%). None of patients discontinued selpercatinib treatment for safety reasons. No new safety concerns were observed, nor where there any treatment-related death. Conclusions: In this real-world setting, the selective RET-inhibitor selpercatinib demonstrated durable systemic and intracranial antitumor activity in RET fusion-positive NSCLC and was well tolerated.

e21693 Background: Fusions involving the REarranged during Transfection ( RET) gene are known oncogenic drivers in non-small cell lung cancer (NSCLC). The patient profile is distinct from a genomically-unselected population of NSCLC patients and may lead to the potentially confounded conclusion that RET fusion-positive patients have a better prognosis. This study characterized clinical outcomes in patients with RET fusion-positive NSCLC versus those without when correcting for known demographic differences. Methods: The Flatiron ClinicoGenomics Database, electronic medical record data linked to Foundation Medicine, Inc genomic test results, was used to identify individuals diagnosed with advanced or metastatic NSCLC who initiated anti-cancer systemic therapy between JAN2011 and JUN2019 in the US. Follow up data were available through JUN2019. Patients were considered RET+ if a fusion was reported and RET- if no fusion was reported. Baseline characteristics and tumor response were compared using Fisher’s exact, chi-squared or t-tests; unadjusted and adjusted COX models were used to compare progression-free survival (PFS) and overall survival (OS). Results: There were 5,807 eligible patients with NSCLC; 46 (0.8%) and 5,761 (99.2%) were RET+ and RET-, respectively. Patients with RET+ tumors were significantly younger (63 vs 67 yrs), better performance status, less likely to have smoking history (37% vs 82%), more likely to have non-squamous tumors (98% vs 76%) (all p < 0.05), and less likely to have ALK, ROS1, KRAS or BRAF alterations, which were each 0% in the RET+ group. There were no differences in total lines of therapy received; treatment regimens were comparable. In unadjusted analyses, patients with RET+ tumors had no significant differences in tumor response (p = 0.17) or PFS (p = 0.06) but significantly better OS outcomes (p = 0.005) from the start of first-line therapy. After adjusting for all available baseline covariates, survival outcomes were not significantly different between RET- and RET+ groups (PFS hazard ratio [HR] = 1.24, 95% confidence interval [CI] = 0.86, 1.78, p = 0.26; OS HR = 1.53, 95% CI = 0.95, 2.44, p = 0.08). Conclusions: Patients with RET fusion-positive NSCLC have different baseline characteristics than patients without these fusions. The unadjusted differences in OS between groups appear to be driven by baseline demographic features and not the presence of the RET fusion, however further research is needed. Conclusions are limited by the rarity of RET fusions in NSCLC and subsequent small sample size.

Solid papillary thyroid carcinoma (SV-PTC) is a rare variant which is mainly observed in young patients with a history of exposure to ionising radiations. Neoplasms belonging to such category generally carry RET-PTC (REarranged during Transfection- Papillary Thyroid Carcinoma) fusions and seem to have a slightly worse prognosis with respect to classical and follicular variants of papillary thyroid carcinoma (PTC), though consistent prognostic and survival data are scarce. SV-PTC should be differentiated from trabecular-insular poorly differentiated thyroid carcinomas, which occur in a different age group and carry a dismal prognosis. These latter tumours do not show the typical nuclear features of PTC and show tumour necrosis with an high mitotic activity. In this report a further case of SV-PTC is described which was associated to Hashimoto’s thyroiditis, a finding never described in the cytological literature up to now for SV-PTC; this association created further differential diagnostic problems. The neoplasm displayed RET-PTC1 fusion.

Preliminary data indicate that tyrosine kinase inhibitors (TKIs) function through rearranged during transfection (RET) in breast cancer. However, TKIs are not specific and can block several receptor tyrosine kinases (RTKs). This study used cell lines and primary breast cancer specimens to determine factors associated with TKI response.Proliferation was assessed after short interfering RNA knockdown with or without sunitinib in breast cancer cell lines by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide). Breast cancer tissue and matched normal breast was obtained from 30 women with invasive breast carcinoma. Gene expression was assessed by reverse transcriptase-polymerase chain reaction. Fresh tissue was treated in vitro with sunitinib or control media for 30 min, and response was assessed by phosphorylation-specific western blot.The RTKs including epidermal growth factor receptor (EGFR), vascular endothelial growth factor receptor (VEGFR1-3), platelet-derived growth factor receptor (PDGFRa/b), and Kit were overexpressed in triple-negative breast tumors relative to HER2- and estrogen receptor-alpha (ERα)-positive tumors and normal breast tissue. Knockdown of EGFR reduced in vitro proliferation in MCF-7 and MDA-MB-231 but not in SKBR-3 or ZR-75-1 breast cancer cells. With the exception of RET, response to sunitinib was independent of RTK expression in all four cell lines. Both ERα-positive and low-EGFR-expressing tumors had an increased in vitro sunitinib response, as determined by alteration of Erk activation. Expression of other RTKs and additional clinical factors were not associated with response.Triple-negative breast cancers overexpress RTKs but have decreased in vitro response to the TKI sunitinib. In addition to RET, TKIs that block EGFR may increase the therapeutic efficacy of TKIs in breast cancer.

Papillary thyroid carcinoma (PTC) is the most common form of thyroid cancer, accounting for greater than 80% of cases. Surgical resection, with or without postoperative radioiodine therapy, remains the standard of care for patients with PTC, and the prognosis is generally excellent with appropriate treatment. Despite this, significant numbers of patients will not respond to maximal surgical and medical therapy and ultimately will die from the disease. This mortality reflects an incomplete understanding of the oncogenic mechanisms that initiate, drive, and promote PTC. Nonetheless, significant insights into the pathologic subcellular events underlying PTC have been discovered over the last 2 decades, and this remains an area of significant research interest. Chromosomal rearrangements resulting in the expression of fusion proteins that involve the rearranged during transfection (RET) proto-oncogene were the first oncogenic events to be identified in PTC. Members of this fusion protein family (the RET/PTC family) appear to play an oncogenic role in approximately 20% of PTCs. Herein, the authors review the current understanding of the clinicopathologic role of RET/PTC fusion proteins in PTC development and progression and the molecular mechanisms by which RET/PTCs exert their oncogenic effects on the thyroid epithelium.

International audience; Background: The presence of single nucleotide polymorphisms (SNPs) in the REarranged during Transfection (RET) gene has been investigated with regard to their potential role in the development or progression of medullary thyroid cancer or pheochromocytomas (PHEO) in patients with the multiple endocrine neoplasia type 2 (MEN2) syndrome. The aim of this study was to evaluate the spectrum of RET variants in France between 2003 and 2013, and to evaluate the impact of SNPs on the MEN2 A phenotype.Methods: In this retrospective cohort study, RET variants were screened in 5109 index cases, and RET pathogenic variants were screened in 2214 relatives. Exons 5, 8, 10, 11, 13, 14, 15, and 16 were characterized by Sanger sequencing. RET pathogenic variants, RET variants with unknown functional significance (VUS), and four RET SNP variants—G691S (rs1799939), L769L (rs1800861), S836S (rs1800862), and S904S (rs1800863)—were characterized and are reported in index cases. In silico analysis and classification following the recommendation of the American College of Medical Genetics and Genomics was performed for RET VUS. Each patient's age at the time of diagnosis, sex, and the endocrine neoplasias present at molecular diagnosis were recorded.Results: Twenty-six single VUS in RET without any well-defined risk profiles were found in 33 patients. Nine of these were considered probably pathogenic, 11 of uncertain significance, and six as probably benign. Three double pathogenic variants found in three patients were classified as pathogenic. A study of the entire cohort showed that patients carrying pathogenic variants or VUS in RET together with PHEO were diagnosed earlier than the others. The presence of the G691S SNP, or a combination of SNPs, increased the risk of developing PHEO but did not modify the date of the diagnosis. No association was found between SNPs and medullary thyroid cancer or hyperparathyroidism.Conclusions: The findings propose a classification of 15 of the 26 VUS in RET without any well-defined risk profiles and suggest that the G691S SNP, or a combination of SNPs, may be associated with the development of PHEO.

3106 Background: Activating receptor-tyrosine kinase rearranged during transfection ( RET) mutations and fusions have been recognized as potent drivers of oncogenesis. Recent identification of highly potent and selective RET inhibitors holds great promise in the management of RET-dependent tumors. Here we present a comprehensive analysis of RET alterations in pan-cancer adult malignancies. Methods: We analyzed 59,347 samples from 56,970 patients available from AACR Project GENIE (Cancer Discov. 2017) database for the prevalence of RET fusions, mutations, and copy number alterations in diverse cancer types. Results: A total of 1414 RET alterations were detected, including 91 fusions (6.4%), 1166 missense mutations (82.5%), 136 truncating mutations (9.6%), and 21 in-frame mutations (1.5%). RET fusions were observed in 0.15% of tumor samples and were most commonly identified in non-small cell lung cancer, thyroid cancer, colorectal cancer, prostate cancer, and gastric cancer (62.6%, 18.6%, 5.5%, 4.4%, 3.3% of identified RET fusions, respectively). RET fusions were significantly co-altered with MAPK3/ERK1 (p=0.045), SETD2 (p=1.36E-07 ), and EIF4E (p=0.045), while there was a negative association between RET fusions and EGFR (p=0.009634) , TP53 (p=0.02267), and KRAS (p=2.53E-05) alterations. Most common RET gene upstream partners were KIF5B, CCDC6, and NCOA4 (42.9%, 24.2%, 7.7% of identified RET fusions, respectively). RET missense mutations were found in 2.0% of tumor samples; 136 (11.7%) of identified missense mutations, including 8 RET gatekeeper V804M/L mutations, were characterized as likely oncogenic, 12 (1.0%) as likely benign, and 1018 (87.3%) as variants of unknown significance using OncoKB database. RET amplifications occurred in 1.5% of tested samples. Conclusions: While RET fusions represent extremely rare events in multiple cancers, RET missense mutations occur in 2% of malignancies. Most RET missense variants are described as variants of unknown significance, limiting the impact of precision oncology for the majority of patients with RET alterations. Further functional characterization of RET variants is warranted. MAPK pathway co-alterations in patents with RET fusions may present a strategy for future therapeutic combinations.

After the discovery of the RET (rearranged during transfection) proto-oncogene functional studies revealed that RET is required for organogenesis and spermatogenesis.1 Activation of RET leads to au...

Objectives: Vandetanib is an oral inhibitor of vascular endothelial growth factor receptor, epidermal growth factor receptor and RET (REarranged during Transfection) signaling. The primary objective of this open-label phase I trial was to determine the maximum tolerated dose (MTD) and recommended dose (RD) of vandetanib in combination with gemcitabine in patients with unresectable, locally advanced or metastatic pancreatic adenocarcinoma (PAC). Methods: Patients received vandetanib (100 or 300 mg/day) plus gemcitabine (1,000 mg/m2 i.v. on days 1, 8 and 15 per 28-day cycle) until disease progression, unacceptable toxicity or withdrawal of patient consent. The MTD was determined by the assessment of dose-limiting toxicity (DLT) during the first 28 days of treatment. Results: Fifteen patients were treated. No DLTs occurred in the first cohort of vandetanib 100 mg (n = 3) and recruitment continued at the 300-mg dose level. At the 300-mg dose, 3 out of 12 patients (including 2 in the expansion cohort) experienced DLTs (aphasia, elevated liver enzymes and neutropenia; all of them grade 3), thus exceeding the MTD. No objective responses were observed, with stable disease being the best response in 78% of evaluable patients. Conclusions: Vandetanib 100 mg/day is the RD in combination with gemcitabine in the treatment of patients with advanced PAC.

e20610 Background: RET rearrangements have been identified in 1-2% of lung adenocarcinomas. The most common fusion is the KIF5B-RET, the function and roles of the RET fusion oncogene, and its downstream signaling molecules remain unclear. Methods: We constructed a tissue microarray (TMA) comprising 581 resected tumor tissues from lung adenocarcinoma patients and investigated them using FISH with RET break-apart and KIF5B-RET SY translocation probes. NanoString’s nCounter technology was used to assay RETtranscripts. We evaluated the protein expressions of RET and RET-related signaling molecules, including p-AKT and p-ERK, using TMA-based IHC staining. Results: Using FISH, we identified 51 cases (8.8%) of RET variants and 10 cases (1.7%) of KIF5B-RET fusion genes among the 581 cases. RET protein expression was lower in the group harboring KIF5B-RET fusion gene than that in the group harboring a wild type RET gene. We found the activating EGFR mutations in 11 (21.6%) cases of 51 RET variants. For the group with KIF5B-RET fusion gene, the expression of p-ERK was significantly lower in EGFR mutation subgroup with presence of RET protein compared to EGFR mutation subgroup with absence of RET protein. For the group with RET rearrangement, there were significant differences in the expression level of p-AKT (P = 0.028) and, p-ERK protein expression was remarkably increased, especially in cases with no RET protein expression. Conclusions: Taken together, the expression of p-ERK protein was meaningfully increased in the RET variants group regardless of RET protein expression. This result suggests that RET inhibitors combined with ERK inhibitors may be an effective treatment strategy for lung adenocarcinoma patients harboring the RET variants.

Several new targeted therapies with multikinase inhibitors targeting vascular endothelial growth factor (VEGF), rearranged during transfection and v-raf murine sarcoma viral oncogene homolog B1 pathways have been tested in clinical trials for radioiodine-refractory differentiated thyroid cancer (DTC) and medullary thyroid cancer (MTC) in the past 10 years.Results of the first phase III trial of VEGF-targeted therapy (sorafenib) in DTC were presented in June 2013, and two phase III trials with VEGF and rearranged during transfection-targeted therapies (vandetanib and cabozantinib) in MTC have led to approval by US Food and Drug Administration in the past 2 years. Whereas such therapies increase median progression-free survival compared to placebo, there is no therapy proven to improve overall survival yet. Significant potential adverse event risks associated with such therapies need to be recognized. Dissemination of knowledge about targeted therapies is critical for various medical specialists as patient care for thyroid cancers is best delivered in a multidisciplinary setting.Successful development of targeted systemic therapies in DTC and MTC in the past 5 years is incredibly exciting in the field and patients with advanced DTC/MTC now have new standard-of-care therapy options.

Less than a decade after the identification of activating mutations of the rearranged during transfection (RET) proto-oncogene in multiple endocrine neoplasia type 2 (MEN-2), a clinical syndrome ch...

Review on RET (Rearranged during transfection), with data on DNA, on the protein encoded, and where the gene is implicated.

All patients with medullary thyroid cancer (MTC) are routinely screened for germline mutations in the rearranged during transfection (RET) proto-oncogene. In this Practice Point commentary, we discuss a cross-sectional study by Machens and Dralle, who performed germline RET proto-oncogene mutation analysis in patients with MTC at a tertiary referral centre in Germany to reveal patterns of familial disease presentation over the generations. The study identified a typical distribution of germline RET mutations (subclassified into three accepted risk categories) in the study population, consistent with the reported literature. The investigators also attempted to obtain data on the time of appearance of RET germline mutations in previous generations of the families. The natural history of MTC and penetrance of specific RET mutations could not be clearly identified in each family because of the cross-sectional nature of the study. Nevertheless, the study re-establishes the importance of routine screening for germline RET mutations in all new cases of MTC.

e19005 Background: Rearranged during Transfection (RET) fusions have been reported in 1-2% of lung adenocarcinomas (LADC), KIF5B-RET fusion being the common variant, and less commonly CCDC6-RET, TR...

Respiratory abnormalities have been described in MASH-1 (mammalian achaete-scute homologous gene) and c-RET (“rearranged during transfection”) mutant newborn mice. However, the neural mechanisms underlying these abnormalities have not been studied. We tested the hypothesis that the MASH-1 mutation may impair c-RET expression in brain stem neurons involved in the control of breathing. To do this, we analyzed brain stem c-RET expression and respiratory phenotype in MASH-1 +/+ wild-type, MASH-1 +/− heterozygous, and MASH-1 −/− knock-out newborn mice during the first 2 h of life. In MASH-1 −/− newborns, c-RET gene expression was absent in the noradrenergic nuclei (A2, A5, A6, A7) that contribute to modulate respiratory frequency and in scattered cells of the rostral ventrolateral medulla. The c-RET transcript levels measured by quantitative RT-PCR were lower in MASH-1 −/− and MASH-1 +/− than in MASH-1 +/+ brain stems ( P = 0.001 and P = 0.003, respectively). Breath durations were shorter in MASH-1 −/− and MASH-1 +/− than in MASH-1 +/+ mice ( P = 0.022) and were weakly correlated with c-RET transcript levels ( P = 0.032). Taken together, these results provide evidence that MASH-1 is upstream of c-RET in noradrenergic brain stem neurons important for respiratory rhythm modulation.

Objective: The purpose of this study was to investigate the value of the expression of the RET oncogene (rearranged during transfection) in papillary thyroid carcinomas (PTC) and its variants in the differential diagnosis of thyroid neoplasias. According to the literature RET oncogene activation by chromosomal rearrangements has been exclusively implicated in PTCs. Methods: To establish the incidence of RET activation in PTCs we used 5- to 10-µm sections from archival paraffin blocks. Either parts of the tissue slices were manually dissected or a few distinct cells were microdissected by laser-mediated manipulation with the Robot-MicroBeam system. RNA was extracted from paraffin-embedded thyroid tumors and the corresponding normal tissue. RT and nested PCR were performed using primers for RET/PTC1, PTC2 and PTC3, or for RET exons 12 and 13. PCR products were resolved by gel electrophoresis. Results: We detected RET transcription in approximately 85% of the PTCs including follicular variants and in isolated cells of the same tissues, but not in nonmalignant thyroid tissue. Conclusions: Our method may serve as an additional diagnostic tool to characterize ambiguous neoplasias and to identify especially nonpapillary, i.e. follicular tumors, as papillary carcinomas. Additionally, this study has demonstrated that expressed genes can be analyzed from routine histopathological tissue slides or pooled single cells. Large retrospective studies can also be performed with this method.