NTRK1 Rearrangements Research Articles

NTRK1 rearrangement in colorectal cancer patients: evidence for actionable target using patient-derived tumor cell line

We have investigated the incidence of NTRK1 rearrangements in metastatic gastrointestinal cancer patients and demonstrated the potential for clinical response of these patients to targeted therapy. We prospectively collected tumor tissue specimens for one year and simultaneously generated patient-derived tumor cells (PDCs). Specimens were initially screened for TrkA protein expression using TrkA immunohistochemistry (IHC). In the case of TrkA IHC positive results, samples were further examined by fluorescence in situ hybridization (FISH) and next generation sequencing (NGS) to confirm the presence of NTRK1 rearrangements. From January 2014 to December 2014, a total of 74 metastatic colorectal cancer (CRC) patients and 66 gastric cancer (GC) patients were initially screened by TrkA IHC. Two of the 74 CRC patients (2.7%) and one of the 66 GC patients (1.5%) were positive for TrkA expression by IHC. All three IHC positive cases had evidence of NTRK1 rearrangements by FISH. NGS was performed on the 3 IHC positive cases and confirmed TPM3-NTRK1 rearrangements in the two CRC cases. One GC patient with TrkA expression by IHC did not harbor an NTRK1 rearrangement. PDCs established from the NTRK1 positive CRC patients were positive for the NTRK1 rearrangement. Entrectinib, a pan-TRK inhibitor, profoundly inhibited cell proliferation of NTRK1-rearranged PDCs with such inhibition associated with inactivation of TrkA, and down-regulation of downstream signaling pathways. TrkA IHC is an effective, initial screening method for NTRK1 rearrangement detection in the clinic. Inhibition of the TrkA kinase is a promising targeted therapy for cancer patients whose tumors harbor a NTRK1 rearrangement.

Abstract 4268: An unbiased survey of cancer-related rearrangements in 5,917 solid tumors identifies therapeutically actionable fusions across multiple disease subtypes

Abstract The growing trend to make cancer treatment more precise depends on the accurate identification of clinically actionable genomic alterations within a patient's tumor. Fusion proteins that result from genomic rearrangements are attractive therapeutic targets because they are tumor-specific and cancer cells depend on their expression for survival. The goal of this study was to investigate the breadth of genomic rearrangements in 19 genes shown to be fused in at least one solid cancer across a collection of 5,917 tumors from a diverse variety of subtypes. All tumor samples were submitted to a CLIA-certified CAP-accredited laboratory (Foundation Medicine, Cambridge MA) for next-generation sequencing-based genomic profiling of 3,769 exons from 236 cancer related genes and 47 introns of 19 genes frequently rearranged in cancer. We observed 350 genomic rearrangements in 338 samples from 82 different solid tumor pathologies. Rearrangements involving kinases were observed in 176 samples (3% of total samples). We identified potentially druggable rearrangements of BRAF (n=13 unique partners; 9 pathologies), ALK (n=11 unique partners; 11 pathologies), FGFR2 (n=9 unique partners; 6 pathologies), ROS1 (n=7 unique partners ; 3 pathologies), RET (n=7 unique partners; 5 pathologies), FGFR3 (n=5 unique partners; 6 pathologies), NTRK1 (n=3 unique partners; 3 pathologies), ERBB2 (n=2 unique partners; 2 pathologies), and ERBB3 (n=2 unique partners; 2 pathologies). ALK, ROS1, RET, and NTRK1 fusions in lung cancer have all shown sensitivity to targeted agents in patients. The largest number of genomic rearrangements (n=87) was found in lung adenocarcinoma (12% of cases). Interestingly, we identified a KIAA1549-BRAF fusion in a triple negative breast cancer sample, a FIP1L1-PDGFRA fusion in glioblastoma, a KIF5B-RET fusion in ovarian cancer, and an NCOA4-RET fusion in colon adenocarcinoma. These fusions have been identified previously in pilocytic astrocytoma, myeloid malignancies, lung cancer and thyroid cancer, respectively, but have rarely been reported outside of these diseases; importantly, hypereosinophilic syndromes harboring FIP1L1-PDGFRA are sensitive to imatinib, and lung cancers with KIF5B-RET are sensitive to cabozantinib. Collectively, these data demonstrate that gene fusions exist across a multitude of tumor types and that known fusions are not always confined to the disease in which they appear most often. These rearrangements include clinically actionable fusions which may identify tumors that are sensitive to selective FDA-approved targeted agents. Citation Format: Juliann Chmielecki, Garrett Frampton, Doron Lipson, Jie He, Geoff Otto, Siraj Ali, Jeffrey S. Ross, Vincent A. Miller, Roman Yelensky, Philip J. Stephens. An unbiased survey of cancer-related rearrangements in 5,917 solid tumors identifies therapeutically actionable fusions across multiple disease subtypes. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4268. doi:10.1158/1538-7445.AM2014-4268

Thyroid Cancer: Molecular Characteristics of Radiation-Associated Papillary Thyroid Cancer, with a Special Reference to of Atomic Radiation Exposure

Among atomic-bomb (A-bomb) survivors of Hiroshima and , incidence of thyroid cancer significantly increased after exposure to nuclear radiation. This review will focus on the initiating gene alterations in the development of adult-onset papillary thyroid cancer (PTC) among A-bomb survivors. The effects of A-bomb radiation on chromosomal rearrangements (RET and NTRK1 rearrangements) and point mutations (BRAF and RAS mutations) after exposure were different. In contrast to PTC cases with point mutations, PTC cases with chromosomal rearrangements were observed more frequently among those exposed to high radiation doses compared to low doses, and these cases developed cancer earlier after exposure than did cases with point mutations. Interestingly, PTC cases with non-detected gene alterations were found more frequently among patients who were exposed to high radiation doses and who developed cancer earlier after radiation exposure than did the cases with BRAF point mutation. This suggests that heretofore non-detected gene alterations may also be involved in adult-onset PTC among A-bomb survivors.

Actionable NTRK1 Rearrangements Occur in NSCLC

Abstract Gene fusions involving NTRK1 (which encodes TRKA) were identified in 3.3% of patients with NSCLC.

Oncogenic and drug-sensitive NTRK1 rearrangements in lung cancer.

We identified novel gene fusions in patients with lung cancer harboring the kinase domain of the NTRK1 gene that encodes the TRKA receptor. Both the MPRIP-NTRK1 and CD74-NTRK1 fusions lead to constitutive TRKA kinase activity and are oncogenic. Treatment of cells expressing NTRK1 fusions with inhibitors of TRKA kinase activity inhibited autophosphorylation of TRKA and cell growth. Three of 91 lung cancer patients (3.3%), without known oncogenic alterations, assayed by NGS or FISH demonstrated evidence of NTRK1 gene fusions.

Abstract 3599: Prevalance and spectrum of chromosomal rearrangements in post-Chernobyl thyroid cancer.

Abstract Introduction: After the Chernobyl disaster, a strong association between childhood I-131 exposure and papillary thyroid carcinoma (PTC) was observed. Our previous study of PTCs from a Ukrainian cohort who were < 18 y.o. at the time of Chernobyl and received 0.008-8.6 Gy of I-131 to the thyroid revealed that RET/PTC rearrangement was the most common mutation and correlated with I-131 dose (Cancer, in press). Common forms of rearrangement and point mutation were detected in 37 (60%) of these tumors. The aim of this study was to examine the remaining tumors for rare rearrangements known to occur in thyroid cancer and for novel chromosomal rearrangements. Design: Twenty-five mutation-negative PTCs were analyzed. RT-PCR was used to search for BRAF/AKAP9 fusion and differential real-time PCR to search for all types of RET and NTRK1 rearrangements. After screening for these rearrangements, RNA from 12 tumors lacking all known mutation or rearrangement were used to create libraries and perform whole RNA sequencing on the Illumina HiSeq2000. Thyroid dose estimation was based on radioactivity measurements, environmental transport models, and interview data. Results: Chromosomal rearrangements and point mutations identified in this cohort are shown, with patient characteristics, in Table 1. Additionally, through RNA-seq, a novel chromosomal rearrangement was identified in several tumors that lack known alteration and were associated with a mean thyroid dose of 2.39 Gy. This novel rearrangement is being validated and characterized. Table 1. Chromosomal rearrangements and corresponding patient characteristics Genetic Alteration Mutation frequency I-131 dose, mean (Gy) Age at exposure, mean (yrs) Latency, mean (yrs) RET/PTC1 and 3 22 (36%) 1.22 6.4 15.9 Other RET/PTC 1 (1.6%) 0.01 11.5 14.2 PAX8/PPARγ 2 (3%) 0.62 12.2 13.5 BRAF/AKAP9 1 (1.6%) 0.27 11.2 20.8 NTRK1 rearrangement 1 (1.6%) 0.44 6.8 15.7 BRAF or RAS mutation 14 (22%) 0.27 10.5 17.6 None (or newly discovered) 22 (35%) 2.05 7.7 16.5 Overall 62 (100%) 1.27 8.1 16.5 Conclusions: Our results demonstrate the occurrence, although with low frequency, of NTRK1, BRAF/AKAP9, and rare types of RET/PTC rearrangements in this post-Chernobyl cohort. In addition, a novel chromosomal rearrangement was identified in tumors associated with high mean I-131 dose, which should further elucidate the genetic mechanisms of radiation-induced thyroid carcinogenesis. Citation Format: Rebecca J. Leeman-Neill, Alina J. Brenner, Mark P. Little, Tetiana Bogdanova, Maureen Hatch, Kiyohiko Mabuchi, Mykola Tronko, Yuri E. Nikiforov. Prevalance and spectrum of chromosomal rearrangements in post-Chernobyl thyroid cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3599. doi:10.1158/1538-7445.AM2013-3599

Impact of pathognomonic genetic alterations on the prognosis of papillary thyroid carcinoma

BRAF mutations and RET or NTRK1 rearrangements were identified as causing events that drive the malignant transformation of the thyroid follicular cell. The impact of these alterations on the course of papillary thyroid carcinoma (PTC) is still unsettled. Tumor tissues of 290 (98 male, 192 female) patients were intra-operatively snap frozen or harvested from archival paraffin-embedded blocks and used for extraction of DNA and RNA. Comprehensive analysis of RET/PTC and NTRK1 rearrangements was carried out by multiplex screening RT-PCR, hybrid-specific RT-PCR and sequencing of detected hybrids. A mutation-specific PCR was used for BRAF analysis. The BRAF V600E mutation was detected in 122/290 (42%), RET rearrangements in 20/137 (14.6%), and NTRK1 rearrangements in 15/93 (16.1%) PTCs. One hundred forty one out of 290 (48.6%) PTCs demonstrated none of the genetic alterations studied. Eight PTCs expressed two different mutations (1 RET/PTC + BRAF, 6 NTRK1 + BRAF, 1 RET/PTC + NTRK1). Tumor-specific survival analysis (mean follow-up, 5.5years) demonstrated no significant difference, but a tendency toward worse prognosis of BRAF-positive patients compared to BRAF-negative patients or rearrangement-positive patients, respectively. Long-term follow-up data on large tumor panels are needed to disclose significant survival differences of prognostic predictors on PTC. This study provides further evidence that patients harboring BRAF-V600E-positive PTCs may experience an unfavorable course of the disease compared to patients with tumors carrying other genetic alterations.

Multiple Genetic Alterations in Papillary Thyroid Cancer are Associated with Younger Age at Presentation

There is a significant gender and age disparity in thyroid cancer incidence and outcome. The molecular basis for these divergent clinical presentations and outcome are essentially unknown. The primary tumor genotype in 217 patients with papillary thyroid cancer was determined for six common somatic genetic alterations (RET/PTC1, RET/PTC3, and NTRK1 rearrangements, and BRAF V600E, KRAS, and NRAS hotspot mutations) by PCR and direct sequencing, and nested PCR. Univariate and multivariate analyses were performed to determine the association of genetic changes and age, gender, and other clinicopathologic factors. One hundred twenty-one of the 190 conventional papillary thyroid carcinoma samples (63.7%) had at least one genetic alteration, and 27 of the samples (14.2%) had more than one alteration. In the follicular variant of papillary thyroid carcinomas, 13 of the 27 samples (48.1%) had at least one genetic alteration and three of the 27 samples (11.1%) had more than one. The presence of multiple genetic alterations was associated with younger age at diagnosis (P=0.034), mean difference of 8 y earlier. We found no significant association with the number or type of genetic alterations present by gender, tumor size, extent of tumor differentiation, multicentricity, lymph node metastasis, distant metastases, TNM stage, and the AMES risk group. The association of multiple genetic alterations and younger age were independent of tumor size, lymph node or distant metastasis, TNM stage, or AMES risk group. Multiple genetic alterations are more common in younger patients with papillary thyroid cancer, but there is no difference in the type or number of genetic alterations by gender. Our findings suggest that multiple genetic alterations in thyroid cancer may be associated with earlier disease initiation and or progression.

Molecular analysis of the RET and NTRK1 gene rearrangements in papillary thyroid carcinoma in the Polish population

Among different genetic factors involved in the pathogenesis of the papillary thyroid carcinoma (PTC), rearrangements of RET protooncogene ( RET/PTC), as well as rearrangements of NTRK1 protooncogene are best known. The resulting hybrid oncogenes are found in PTCs with variable frequency, depending on the examined population. The relationship between these chromosomal aberrations and clinical outcome of PTCs remains still controversial. The study aimed at estimating the frequency of rearrangements of RET and/or NTRK1 protooncogenes in PTC in the Polish population, and at evaluating the possible relationships between the presence of RET and/or NTRK1 oncogenes and such parameters, as patient's age, gender, histopathological variant of tumor and clinical staging. Expression analysis of RET and NTRK1 was performed by duplex reverse transcription-polymerase chain reaction (duplex RT-PCR) and OneStep RT-PCR, respectively, in tumor tissues obtained from 33 patients with PTC. Rearrangements of the RET protooncogene ( RET/PTC1, RET/PTC2 and RET/PTC3) were detected in 7 out of 33 PTC (21%), and rearrangements of NTRK1 [ Trk–T1 and Trk( TPM3)] were detected in 4 out of 33 examined samples (12%). In none of the examined cases, did the RET and NTRK1 rearrangements occur in the same sample. No correlations were found between RET/PTC or Trk oncogenic sequences and patient's age, gender, the histopathological variant of PTC and the assignment to particular stage in clinical staging systems (TNM Staging, the University of Chicago clinical class, and Ohio State University Staging). Our study is the first one in which the frequency of NTRK1 rearrangements in PTC was reported for the Polish population. On the other hand, the frequency of RET rearrangements in PTC, as found by us, was similar to the previously reported results for the Polish population. Our results do not confirm the relationship between the structural aberrations in question and the clinical outcome of PTC.

Oncogenic rearrangements of the NTRK1/NGF receptor

The NTRK1 gene encodes the high affinity receptor for Nerve Growth Factor, and its action regulates neural development and differentiation. Deregulation of NTRK1 activity is associated with several human disorders. Loss of function mutations causes the genetic disease congenital insensitivity to pain with anhidrosis (CIPA). Constitutive activation of NTRK1 has been detected in several tumor types. An autocrine loop involving NTRK1 and NGF is associated with tumor progression in prostate carcinoma and in breast cancer. A novel alternative splicing variant with constitutive oncogenic potential has been recently described in neuroblastoma. Somatic rearrangements of NTRK1, producing chimeric oncogenes with constitutive tyrosine kinase activity, have been detected in a consistent fraction of papillary thyroid tumors. The topic of this review is a detailed analysis of the thyroid TRK oncogenes. The modalities of their activation, their mechanism of action, the contribution of activating sequences, and the molecular mechanisms underlying their generation will be discussed.

No correlation between BRAFV600E mutation and clinicopathological features of papillary thyroid carcinomas in Taiwan

Genetic alterations in four oncogenes, namely RAS point mutations, RET rearrangements (RET/PTC), NTRK1 rearrangements (TRK) and BRAF point mutations have been identified in human papillary thyroid carcinomas (PTCs). These oncogenes act along the RET/PTC(TRK)-RAS-BRAF-MEK-MAPK kinase pathway, mediating a number of cellular fates including growth, proliferation and survival in thyroid cells. In this study, we analysed mutations of BRAF in a cohort of PTCs. To screen for BRAF mutations, the genomic DNA of 105 PTCs were amplified by polymerase chain reaction (PCR) with primers flanking exon 15 and PCR products were directly sequenced with an automatic sequencer. These results, together with data from our previous studies on RAS, RET rearrangements and NTRK1 rearrangements in the same tumours, were compared to determine their individual significance in the pathogenesis of PTCs in Taiwan. BRAF mutations were detected in 49 of 105 (47%) tumour samples. All mutations involved a thymine-to-adenine transversion at nucleotide 1799 and were heterozygous. There was no overlap between papillary carcinomas harbouring RET rearrangements, NTRK1 rearrangements and BRAF mutations. In this cohort, correlation between BRAF mutations and various clinicopathological parameters in 101 papillary carcinomas did not reveal any association with age at diagnosis, sex, tumour size, histological variants of PTC, multicentricity, cervical lymph node metastases, extrathyroidal invasion, distant metastases and clinical stage. BRAFV600E mutation is the most prevalent oncogene in PTCs in Taiwan. Our data did not suggest that BRAFV600E mutation could be a potentially useful marker of prognosis in patients with papillary carcinomas in the population studied.

Alternative mutations of BRAF, RET and NTRK1 are associated with similar but distinct gene expression patterns in papillary thyroid cancer.

Papillary thyroid carcinoma (PTC) is associated with RET and NTRK1 rearrangements and BRAF mutations. A series of 60 PTCs collected in a single center from Italian patients were histologically re-examined and subclassified as well differentiated or tall cell variant. The sample collection was analysed for the presence of all the reported PTC-associated genetic alterations through DNA or cDNA amplification, followed by automated sequencing. The analysis of exons 11 and 15 of BRAF gene revealed the T1796A (V599E) mutation in 32% of cases, and this alteration is significantly associated with PTC tall cell variant. Oncogenic rearrangements of RET and NTRK1 receptors were found in 33 and 5% of cases, respectively. No Ras mutations were detected. Overall, genetic alterations were detected in two-thirds of samples, and in no single case more than one mutational event was found simultaneously. Gene expression profiling of a subset of 31 tumors performed using cDNA microarray chips showed no strong differences in global gene expression among the different cases. However, a supervised analysis of the obtained data identified a subset of genes differentially expressed in tumors carrying BRAF mutation or RTK rearrangement.

Gene rearrangements in thyroid carcinomas after irradiation during childhood: lessons from the Chernobyl reactor accident

Papillary thyroid carcinomas (PTC) developed with a high incidence in children and young adults who had been exposed to radioactive fallout in contaminated regions of Belarus after the Chernobyl reactor accident. They are informative for a molecular genetic analysis of radiation-induced PTC. In contrast to spontaneous PTC, a high prevalence of gene aberrations was found with rearrangements of the receptor tyrosine kinase gene RET in the majority of cases and a few NTRK1 rearrangements. In the rearranged form of RET, the transmembrane and extracellular parts are replaced by regulatory units of other genes. Among the fused genes, ELE1 ( ARA70) is most prevalent in PTC at short latency periods after irradiation, H4 gene fusions prevail in later-occurring PTC. Both types of rearrangement, PTC3 and PTC1, respectively, are formed by intrachromosomal inversions on chromosome 10. Analysing ELE1/ RET chimeric genes, we found radiation-induced DNA breakpoints localized exactly at or in close vicinity to topoisomerase I binding sites indicating a role for this enzyme in the formation of DNA breaks after irradiation. Breakpoints are distributed in the affected introns of both genes without significant clustering. They do not contain larger deletions of insertions. Short regions of sequence homology and short direct or inverted repeats were observed at the breakpoints suggesting microhomology-mediated DNA end joining as a mechanism in the fusion process. In addition to PTC1 and PTC3, we and others described several rare novel types of RET rearrangement, all formed by interchromosomal translocations, with parts of RIα, GOLGA5, HTIF, RFG7, RFG8, KTN1, and ELKS fused at the 5' end of the RET tyrosine kinase domain. These gene fusions appear to have in common an uncoupling of the RET tyrosine kinase from its physiological control due to an inherent dimerization potential. This may lead to constitutive, ligand-independent activation of RET tyrosine kinase in thyrocytes lacking this activity under normal conditions, and subsequent clonal expansion of the affected cells. It is evident from our comparative study on a large number of PTC with ELE1/ RET and H4/ RET rearrangements after irradiation that the type of the RET-fused gene determines the tumor phenotype and may be decisive also for the clinical course of radiation-induced PTC.

Prognostic significance of RET and NTRK1 rearrangements in sporadic papillary thyroid carcinoma

Background. The expression of RET/PTC chimeras was demonstrated in 10% to 20% of sporadic papillary thyroid carcinomas (PTCs), whereas rearrangements of NTRK1 were detected less frequently. Some investigators have hypothesized that RET/PTC activation is preferentially associated with slow-growing tumors of low malignancy in elderly patients; other studies support the contrary. Methods. Expression analysis of RET and NTRK1 was performed by duplex reverse transcription-polymerase chain reaction in tumor tissues from 119 patients with PTC. Samples with suspected rearrangements were further analyzed for the expression of the hybrid messenger RNAs RET/PTC 1 to RET/PTC 7 and for known NTRK1 chimeras, respectively. Results. Seventeen of 119 tumors (14.3%) revealed somatic rearrangements of RET; NTRK1-derived hybrids were demonstrated in 15 cases (12.6%). In patients with RET/PTC chimeras, a statistically not significant tendency towards younger age, lower recurrence rate, and improved survival was observed, despite increased incidence of lymph node metastasis. Cumulative survival analysis of NTRK1 rearrangement-positive individuals demonstrated a worse outcome when compared with patients with expression of RET hybrids (P =.055). Conclusions. The high incidence of yet uncharacterized NTRK1 hybrid mRNAs in our patient cohort leads to the speculation that activating chromosomal rearrangements of several tyrosine kinase receptors may be a common feature of PTCs and that the expression of distinct chimeras may potentially be of prognostic significance. (Surgery 2000;128:984-93.)

Prognostic significance of RET and NTRK1 rearrangements in sporadic papillary thyroid carcinoma

Abstract Background The genetic background of papillary thyroid carcinoma (PTC) has been elucidated by the identification of somatic translocations of the tyrosine kinases RET and NTRK1. Expression of RET/PTC chimeras has been demonstrated in 10–25 per cent of sporadic PTCs while rearrangements of NTRK1 were detected less frequently. Based upon the limited data available, some investigators have hypothesized that RET/PTC activation is preferentially associated with slow growing tumours of low malignancy in elderly patients, while other studies support the contrary. Methods Tumour tissues from 115 patients with sporadic PTC were harvested at operation and snap frozen. Following RNA extraction, expression analysis of the RET proto-oncogene as well as the NTRK1 gene was performed by multiplex reverse transcriptase–polymerase chain reaction. Samples with suspected rearrangements of the genes were further analysed for expression of the hybrid messenger RNAs RET/PTC1 to RET/PTC4, and for known NTRK1 chimeras. Clinical data of all patients were documented in an extensive database of thyroid carcinomas maintained by this research group. Results Twenty-one (18 per cent) of 115 tumour samples revealed somatic rearrangements of RET while translocations of the NTRK1 gene were demonstrated in 2 per cent of all samples analysed to date. The mean age of all patients was 52 (range 14–86, median 54) years and that of patients positive for RET rearrangements was 49 (range 14–82, median 49) years. Nine of 21 RET-rearranged tumours showed aggressive behaviour with locally invasive tumour growth and infiltration of adjacent structures such as muscles, vessels and trachea. Tumour samples without detectable RET translocations were associated with organ-exceeding tumour growth in only 20 per cent of cases. Conclusion These data represent one of the most comprehensive studies on gene translocations and their clinical significance in PTC. In accordance with international publications, an incidence of 2 per cent of NTRK1 rearrangements and 18 per cent of RET translocations is reported, which is in contrast to other national reports of low rearrangement rates. Somatic translocations were associated with tumours demonstrating aggressive behaviour in almost half of patients with PTC in all age groups, indicating a prognostic role of oncogenic RET/PTC activation.

Search for NTRK1 proto-oncogene rearrangements in human thyroid tumours originated after therapeutic radiation.

Rearrangements of NTRK1 proto-oncogene were detected in ‘spontaneous’ papillary thyroid carcinomas with a frequency varying from 5 to 25% in different studies. These rearrangements result in the formation of chimaeric genes composed of the tyrosine kinase domain of NTRK1 fused to 5′ sequences of different genes. To investigate if the NTRK1 gene plays a role in radiation-induced thyroid carcinogenesis, we looked for the presence of NTRK1 -activating rearrangements in 32 human thyroid tumours (16 follicular adenomas, 14 papillary carcinomas and two lymph-node metastases of papillary thyroid carcinomas) from patients who had received external radiation, using the reverse transcription polymerase chain reaction, Southern blot and direct sequencing techniques. These data were compared with those obtained in a series of 28 ‘spontaneous’ benign and malignant thyroid tumours, collected from patients without a history of radiation exposure and four in vitro culture cell lines derived from ‘spontaneous’ thyroid cancers. Our results concerning the radiation-associated tumours showed that only rearrangements between NTRK1 and TPM3 genes (TRK oncogene) were detected in 2/14 papillary carcinomas and in one lymph-node metastasis of one of these papillary thyroid carcinomas. All the radiation-associated adenomas were negative. In the ‘spontaneous’ tumours, only one of the 14 papillary carcinomas and one of the four in vitro culture cell lines, derived from a papillary carcinoma, presented a NTRK1 rearrangement also with the TPM3 gene. Twenty-five of this series of radiation-associated tumours were previously studied for the ras and RET/PTC oncogenes. In conclusion, our data: (a) show that the overall frequency of NTRK1 rearrangements is similar between radiation-associated (2/31: 6%) and ‘spontaneous’ epithelial thyroid tumours (2/32: 6%). The frequency, if we consider exclusively the papillary carcinomas, is in both cases 12%; (b) show that the TRK oncogene plays a role in the development of a minority of radiation-associated papillary thyroid carcinomas but not in adenomas; and (c) confirm that RET/PTC rearrangements are the major genetic alteration associated with ionizing radiation-induced thyroid tumorigenesis. © 2000 Cancer Research Campaign

Low frequency of rearrangement of TRK protooncogene in Chinese thyroid tumors.

The TRK protooncogene (NTRK1) encodes a cell-surface transmembrane tyrosine kinase (TK) acting as a receptor for nerve growth factor. Oncogenic potential in thyrocytes results from replacing the 5' portion by regulatory parts of other genes, leading to constitutive TK expression. In Italy, human papillary thyroid carcinoma (PTC) shows a frequent activation (50%) of the TK receptor genes NTRK1 and RET. Both genes undergo oncogenic rearrangements by the same mechanism. We previously reported high frequency (6/11) of rearrangement of the RET protooncogene in Chinese PTCs. Wide differences in the frequency (0-10.9%) of the NTRK1 rearrangement in PTCs have been reported in different populations. To investigate the frequency of TRK protooncogene rearrangement in Chinese thyroid tumors, we performed reverse transcriptase polymerase chain reaction to amplify specific TRK rearrangement transcripts. We examined thyroid tumors of 40 patients, including 14 papillary carcinomas, 4 follicular carcinomas, 1 Hurthle cell carcinoma, 1 insular carcinoma, and 20 nodular goiters. NF874 NIH3T3, NF723 NIH3T3, NF861 NIH3T3, and NF881 NIH3T3 were used as controls for TRK-T3, TRK-T2, TRK-T1, and TRK, respectively. No known TRK protooncogene rearrangements were detected among the 40 thyroid tumors in our studies. We suggest that the TK receptor NTRK1 activation seems less important than RET activation in PTCs in the Chinese population.

NTRK1 re-arrangement in papillary thyroid carcinomas of children after the Chernobyl reactor accident.

The prevalence of NTRK1 re-arrangement was determined in papillary thyroid carcinomas (PTCs) of children from Belarus who had been exposed to radioactive iodine after the Chernobyl reactor accident; 81 tumors were included, all of which were devoid of RET re-arrangement as analyzed in a current study on genomic alterations in PTC. Oncogenic fusion of the NTRK1 tyrosine kinase domain with the amino-terminal part of the tropomyosin gene (TPM3/NTRK1, trk) was observed in 5 tumors. A single tumor exhibited a TPR/NTRK1 fusion (TRK-T2). Reciprocal NTRK1/TPM3 transcripts were found in 4 of 5 tumors with TPM3/NTRK1 re-arrangement, indicating an intra-chromosomal balanced reciprocal inversion. No phenotypic differences from other post-Chernobyl childhood PTCs were detected. As compared with the high prevalence of RET re-arrangements reported for thyroid carcinomas of children after the Chernobyl reactor accident, NTRK1 re-arrangements appear rare. Our results confirm that activation of receptor tyrosine kinase genes plays the predominant role in post-Chernobyl childhood thyroid carcinogenesis.

NTRK1 re‐arrangement in papillary thyroid carcinomas of children after the Chernobyl reactor accident

The prevalence of NTRK1 re-arrangement was determined in papillary thyroid carcinomas (PTCs) of children from Belarus who had been exposed to radioactive iodine after the Chernobyl reactor accident; 81 tumors were included, all of which were devoid of RET re-arrangement as analyzed in a current study on genomic alterations in PTC. Oncogenic fusion of the NTRK1 tyrosine kinase domain with the amino-terminal part of the tropomyosin gene (TPM3/NTRK1, trk) was observed in 5 tumors. A single tumor exhibited a TPR/NTRK1 fusion (TRK-T2). Reciprocal NTRK1/TPM3 transcripts were found in 4 of 5 tumors with TPM3/NTRK1 re-arrangement, indicating an intra-chromosomal balanced reciprocal inversion. No phenotypic differences from other post-Chernobyl childhood PTCs were detected. As compared with the high prevalence of RET re-arrangements reported for thyroid carcinomas of children after the Chernobyl reactor accident, NTRK1 re-arrangements appear rare. Our results confirm that activation of receptor tyrosine kinase genes plays the predominant role in post-Chernobyl childhood thyroid carcinogenesis. Int. J. Cancer 80:842–847, 1999. © 1999 Wiley-Liss, Inc.