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Background: Myxoid liposarcomas (MLS) can exhibit a disseminated metastatic pattern, necessitating extensive diagnostics during follow-up. With no tumor markers available, early diagnosis of recurrences and tumor monitoring is difficult. The detection of circulating tumor DNA (ctDNA; liquid biopsy) in MLS with the characteristic translocations t(12;16) and t(12;22) can provide an additional diagnostic. However, due to the often very low tumor fraction, distinguishing actual tumor variants from sequencing artifacts remains a key challenge., Methods: Using MLS as a model for translocation-driven tumors, this study evaluates a refined analytical approach for detecting both single nucleotide variants (SNVs) and structural variants (SVs) with the highest possible sensitivity and specificity. Different analysis pipelines using Unique Molecular Identifiers (UMIs) were compared in dilution series of tumor DNA from MLS patients (n = 11) and a cell line. The results were validated on plasma samples (n = 36) from two MLS patients and one patient with Synovial Sarcoma (SS)., Results: In dilution series, the use of UMIs significantly reduced false positive events in SNV analysis while maintaining high sensitivity without significant differences. In SV analysis, the effect of UMIs was not consistently detectable, as some dilution series exhibited no false positive events even without UMI correction. Additional filter criteria further improved specificity without significantly compromising assay sensitivity. Validation on patient plasma samples confirmed these findings, demonstrating the advantages of the differentiated analytical approach., Conclusion: By integrating a refined analytical approach for SNVs and SVs, we achieved reliable ctDNA detection that corresponded with the clinical course of the patients' disease. This method enables non-invasive tumor detection in translocation-driven tumors with low mutational burden and can easily be adapted into routine clinical diagnostics., (© 2025 The Author(s). Cancer Medicine published by John Wiley & Sons Ltd.)

Myxoid liposarcoma has the pathognomonic fusion oncogene FUS-DDIT3 encoding a chimeric transcription factor. Metastatic risk is higher with an increased round cell component and has been linked to aberrations involving the IGFR/PI3K/AKT pathway. These molecular insights have yet to translate to targeted therapies, and the lack of experimental models is a major hindrance. We describe the initial in-depth characterization of a new cell line (DL-221) and establishment of a mouse xenograft model. The cell line DL-221 was derived from a metastatic pleural lesion showing myxoid and round cell histology. This newly established cell line was characterized for phenotypic properties and molecular cytogenetic profile, using PCR, COBRA-FISH, and western blot. Next-generation whole-exome sequencing was performed to further characterize the cell line and the parent tumor. NOD-SCID-IL2R gamma knockout mice were xenograft hosts. DL-221 cells grew an adhering monolayer and COBRA-FISH showed an aneuploid karyotype with t(12;16)(q13;p11) and several other rearrangements; RT-PCR demonstrated a FUS-DDIT3 fusion transcript type 1. Both the cell line and the original tumor harbored a TP53 compound heterozygous mutation in exon 4 and 7, and were wild-type for PIK3CA. Moreover, among the 1254 variants called by whole-exome sequencing, there was 77% concordance between the cell line and parent tumor. The recently described hotspot mutation in the TERT promoter region in myxoid liposarcomas was also found at C228T in DL-221. Xenografts suitable for additional preclinical studies were successfully established in mice after subcutaneous injection. The established DL-221 cell line is the only published available myxoid liposarcoma cell line that underwent spontaneous immortalization, without requiring SV40 transformation. The cell line and its xenograft model are unique and helpful tools to study the biology and novel potential-targeted treatment approaches for myxoid liposarcoma.

Myxoid liposarcomas are malignant lipomatous tumors with a predilection for young adults. They are characterized by the presence of reciprocal translocation between the CHOP (DDIT3) gene on chromosome 12 and the FUS gene on chromosome 16, t(12;16)(q13;p11.2) in >95% of cases, or less commonly, a translocation between the DDIT3 and EWSR1 genes, t(12;22)(q13;q12). Secondary aberrations involving trisomy 8 and chromosomes 1 and 16 have been reported. Herein, we report for the first time a novel secondary clonal translocation, t(2;4) (q23;p14) in addition to t(12;16)(q13; p11.2) in a 30-year-old woman with myxoid liposarcoma on the left posterior thigh region without any prior chemoradiation therapy. The significance of this translocation remains to be established.

For the detection of chromosome translocations/chimeric genes and specific genetic abnormalities in soft tissue tumors, we conducted fluorescence in situ hybridization (FISH) analysis on 280 cases of soft tissue and other tumors using formalin-fixed paraffin-embedded tissue sections. The detection rate of the FISH split-signal was 84% (129/154 cases) for the translocation-associated soft tissue tumors, such as Ewing's sarcoma/primitive neuroectodermal tumor, synovial sarcoma, alveolar rhabdomyosarcoma, myxoid liposarcoma, clear cell sarcoma and so forth. Positive split-signals from EWSR1, SS18 and FOXO1A probes were detected in 3% (2/64) of various histological types of carcinoma, lymphoma, melanoma, meningioma and soft tissue tumors. In FISH using the INI1/CEP22 probe, the INI1 deletion signal was detected in 100% (9/9) of epithelioid sarcoma. In well-differentiated and dedifferentiated liposarcomas, detection of MDM2 amplification signals in FISH using the MDM2/CEP12 probe were both as high as 85% (11/13) and 100% (13/13), respectively. In other adipocytic and non-adipocytic tumors requiring differentiation from these types, detection was only 13% (5/39), and CEP12 polysomy was frequently detected. As these results demonstrate the high sensitivity and specificity of FISH, we concluded FISH to be a useful pathological diagnostic adjunct for definite and differential diagnosis of soft tissue tumors., (© 2011 The Authors. Pathology International © 2011 Japanese Society of Pathology and Blackwell Publishing Asia Pty Ltd.)

Aims: To analyse the characteristic sequence motifs around genomic breakpoints of translocations, t(12;16) and t(12;22), and to study the mechanisms underlying these chromosomal translocations in myxoid liposarcomas (MLS)., Methods: Genomic DNA sequences derived from t(12;16) and t(12;22) were amplified by long-distance polymerase chain reaction (PCR) in six cases of MLS, and the DNA sequences around the breakpoints were analysed., Results: Genomic sequences of the FUS-CHOP or EWS-CHOP fusion gene were amplified in five and one MLS, respectively. Our sequence analysis revealed that the gene fusions were generated between intron 1 of the CHOP and either intron 5 (type II) or 7 (type I), or 8 (type III) of the FUS, or intron 7 of the EWS. The breakpoints in intron 1 of the CHOP were located near or within Alu repetitive sequences in the six cases. Sequences homologous to consensus recognition motifs of Translin were present adjacent to the breakpoints in the FUS, EWS, and CHOP genes. Sequences homologous to the topoisomerase II consensus site and palindromic oligomer sequences were also frequently found around the breakpoints in these genes. Moreover, Chi or Chi-like sequences were found in three cases, alternating purine-pyrimidine tracts and polyadenine/polythymine sequences were each found in one case., Conclusions: Our results suggest that characteristic sequence motifs located at the FUS, EWS and CHOP breakpoint regions, including Alu and palindromic oligomer sequences, are involved in the mechanisms creating chromosomal translocations in MLS.

Several previous studies have demonstrated the lack of SMARCB1/INI1 protein expression in only the malignant rhabdoid tumor (MRT). Several sarcoma groups are associated with a tumor-specific translocation involving EWS. Moreover, the EWS and SMARCB1/INI1 genes are located on the same 22q chromosome. We analyzed the status of SMARCB1/INI1 protein expression in 93 cases of sarcomas associated with chromosomal translocation involving EWS, comprising 52 Ewing's sarcoma/primitive neuroectodermal tumors, 24 extraskeletal myxoid chondrosarcomas (EMCS), 14 clear cell sarcomas of soft tissue, 2 desmoplastic small round cell tumors, and 1 myxoid/round cell liposarcoma. In addition, we analyzed the detailed SMARCB1/INI1 gene alteration in cases, which lacked its protein expression. Consequently, 4 EMCS showed no SMARCB1/INI1 expression, and 2 of these 4 cases revealed homozygous deletion and frameshift mutation of the SMARCB1/INI1 gene, respectively. These cases showed histologic findings compatible with EMCS, according to the most recent WHO classification, but no major fusion gene transcripts were detected. Moreover, 3 out of 4 SMARCB1/INI1 negative variant EMCS disclosed rhabdoid features. Therefore, the lack of SMARCB1/INI1 protein expression may be associated with rhabdoid features. The immunohistochemical result of the SMARCB1/INI expression is not an absolute diagnostic criteria for MRT and careful histologic evaluation is required to make a precise diagnosis of MRT.

The clinical course of myxoid/round cell liposarcoma (MRCL) is characterized by frequent local recurrences and metastases at unusual sites. MRCLs carry specific translocations, t(12;16) or rarely t(12;22), linking the FUS or the EWSR1 gene with the DDIT3 gene, respectively. Nine FUS/DDIT3 and three EWSR1/DDIT3 variants of fusion transcripts have been described thus far. In search of prognostic markers for MRCL, we analyzed the translocation types of 31 patients and related them to the event free and overall survival. Using break-apart FISH and RT-PCR combined with DNA sequencing, we detected FUS/DDIT3 fusions in 30 sarcomas, while an EWSR1/DDIT3 translocation was identified in one tumor. FUS/DDIT3 type II (exons 5-2) was most commonly detected (20 cases), followed by type I (7-2) (7 cases) and type III (8-2) (3 cases). A single tumor carrying a t(12;22) translocation expressed a hitherto unknown EWSR1-DDIT3 fusion transcript (13-3) linking the complete RNA-binding domain of EWSR1 with a short piece of the 5'-UTR and the entire open reading frame of the DDIT3 gene. Interestingly, five of six patients with type I (7-2) FUS/DDIT3 fusions displayed local recurrences and/or metastatic spread within the first 3 years, generally requiring chemotherapeutical treatment (median disease-free survival 17 months). In contrast, 9 of 13 patients with type II FUS/DDIT3 translocations remained at 3 years disease-free (median disease-free survival 75 months). Since the total number of patients is still limited, further studies are required to verify a putative association of type I FUS/DDIT3-fusion transcripts with a prognosis of MRCL., (Copyright (c) 2007 Wiley-Liss, Inc.)

Malignant adipose tissue tumors, also called liposarcomas, are the most common sarcoma of adult life. They may be hard to distinguish from benign adipose tissue tumors as well as from other types of sarcomas. Well-differentiated liposarcomas and myxoid liposarcomas are the two histological subtypes that have been best characterized at the genetic level. The defining genetic features of well-differentiated liposarcoma cells are supernumerary circular ("ring") and giant linear rod chromosomes. These rings and giant chromosomes contain amplification of the 12q14-15 region, including the MDM2 gene, associated with coamplification of various other chromosomal regions. In addition, they most often lack alpha-satellite centromeric sequences. The detection of MDM2 amplification is a valuable tool for the differential diagnosis between well-differentiated liposarcomas and lipomas. Dedifferentiated liposarcomas usually present with patterns of MDM2 amplification similar to those observed in well-differentiated liposarcomas. In addition, recent CGH-array studies suggest that co-amplification of MDM2 with the 6q23-25 region might be a specific feature. Myxoid and round-cell liposarcomas are characterized by a translocation t(12;16)(q13;p11) that fuses the DDIT3 and FUS genes. A rare variant translocation t(12;22) that fuses DDIT3 with EWS has also been described. The genetics of pleomorphic liposarcoma is still obscure. Pleomorphic liposarcomas show complex karyotypes with many numerical and structural chromosomal aberrations. To date, no specific molecular abnormality has been identified.

In myxoid/round cell liposarcoma, the t(12;16)(q13;p11) and its associated fusion transcript, FUS-CHOP, characterize greater than 95% of cases. The variant translocation t(12;22)(q13;q12) and associated EWS-CHOP fusion transcript are rare. A second non-random aberration observed in roughly 20% of Ewing's sarcomas, and to a lesser extent other select sarcomas, is the unbalanced 1;16 translocation. Recognition of this secondary aberration in the absence of an obvious primary karyotypic abnormality strongly suggests that the use of other genetic approaches will be informative in uncovering a clinically suspected primary anomaly. The following case illustrates the utility of molecular cytogenetic and reverse transcriptase-polymerase chain reaction techniques in diagnosing an ins(22;12)(q12;q13q14) and associated EWS-CHOP fusion transcript in a myxoid/round cell liposarcoma exhibiting a der(16)t(1;16)(q11;q11).

The cytogenetic hallmark of myxoid liposarcoma is the chromosomal aberration t(12;16)(q13;p11), which is pathognomonic for this tumor type. The translocation results in the hybrid gene FUS/CHOP, where the central and C-terminal parts of FUS, coding for the RNA binding domain and the RGG triplet motif, are replaced by the full length CHOP protein. Thus, CHOP is under the control of the FUS promoter and the FUS/CHOP chimera contains the 5'-terminal part of FUS which provides a transcriptional activation function. Although different structural variations of the FUS/CHOP chimeric transcript have been reported, none of them contains the parts of FUS encoding the RNA binding properties. An explanation is the location of the genomic breakpoint in FUS, which frequently occurs in the region spanning exon 5 to intron 8. We describe here a case of myxoid liposarcoma containing two novel FUS/CHOP chimeric transcripts and with the breakpoint occurring in intron 14 of FUS. Reverse transcription-polymerase chain reaction, using FUS forward and CHOP reverse primers, amplified strongly a 2.1-kbp DNA fragment and weakly a 0.9-kbp DNA fragment. Direct sequencing showed that in the 2.1-kbp transcript nt 1474, which corresponds to the third nucleotide of exon 14 of FUS, was in-frame fused to exon 2 of CHOP. In the 0.9-kbp DNA fragment, exon 3 of FUS was in-frame fused to exon 2 of CHOP. Genomic analyses revealed that the breaks were located at the end of exon 14/beginning of intron 14 of FUS and in intron 1 of CHOP and that microdeletions had occurred in the close vicinity of the breakpoints.

Myxoid and round-cell liposarcomas share the translocation t(12;16)(q13;p11) creating the TLS-CHOP fusion gene as a common genetic alteration. We previously reported several unique characteristics of genomic sequences around the breakpoints in the TLS and CHOP loci, and among them was the presence of consensus recognition motifs of Translin, a protein that associates with chromosomal translocations of lymphoid neoplasms. We further extended our search for Translin binding motifs in sequences adjacent to breakpoints and investigated whether Translin binds to these sequences in vitro by mobility-shift assay. Computer-assisted search found sequences highly homologous (>70%) with Translin binding motifs adjacent to the breakpoints in 10 out of 11 liposarcomas with the TLS-CHOP fusion genes. All of 13 oligonucleotides corresponding to the putative binding sequences in these cases bind to Hela cell extract and also recombinant Translin protein, although the binding affinity of each motif showed considerable differences. The DNA-protein complex formation was inhibited by non-labeled competitor or anti-Translin antibody, suggesting the specificity of the complex formation. Considering the high incidence and specific binding property, the presence of Translin binding motif may be one of the important determinants for the location of breakpoints in the TLS and CHOP genes in liposarcomas.

Fusion of TLS/FUS and CHOP gene by reciprocal translocation t(12;16)(q32;q16) is a common genetic event found in myxoid and round-cell liposarcomas. Characterization of this genetic event was performed by three methods, Southern blot, RT-PCR, and genomic long-distance PCR in nine myxoid and three round-cell liposarcomas. All but one tumors showed genetic alternations indicating the fusion of TLS/FUS and CHOP gene. Two novel types of fusion transcripts were found, of which one lacked exon 2 sequence of CHOP gene, and the other lacked 3' half of exon 5 of TLS gene. The latter case was caused by a cryptic splicing site which was created by the genomic fusion. Detailed analyses genomic fusion points revealed several sequence characteristics surrounding the fusion points. Homology analyses of breakpoint sequences with known sequence motifs possibly involve in the process of translocation uncovered Translin binding sequences at both of TLS/ FUS and CHOP breakpoints in two cases. Translocations were always associated with other genetic alterations, such as deletions, duplications, or insertions. Short direct repeats were almost always found at both ends of deleted or duplicated fragments some of which had apparently been created by joining of sequences that flank the rearrangement. Finally, consensus topoisomerase II cleavage sites were found at breakpoints in all cases analysed, suggesting a role of this enzyme in creating staggered ends at the breakpoint. These data suggested that sequence characteristics may play an important role to recruit several factors such as Translin and topoisomerase II in the process of chromosomal translation in liposarcomas.

The reciprocal translocation t(12;16)(q13;p11) has been shown to be highly characteristic of myxoid and round cell subtypes of liposarcoma, and the TLS/FUS-CHOP fusion gene that resulted from the translocation is expected to be a diagnostic molecular marker of these sarcomas. In this study, we conducted a nested reverse transcription-polymerase chain reaction (RT-PCR)-based assay to detect the TLS/FUS-CHOP fusion gene transcripts using archival formalin-fixed, paraffin-embedded tumor specimens. Of 18 paraffin-embedded specimens from 16 myxoid and round cell liposarcoma cases, the fusion transcripts could be identified in 16 (89%) specimens from 15 (94%) cases. A sequence analysis using the PCR products confirmed that the detected messages were derived from either type I or type II TLS/FUS-CHOP fusion gene, the latter of which was predominant (80%). The results were consistent in primary and recurrent lesions of the same patients and in paraffin-embedded and snap-frozen samples from the same tumors. In two negative specimens, transcripts of the beta-actin gene could not be detected by RT-PCR, and intact mRNA including the fusion messages might have been degraded. No fusion transcripts were detected in snap-frozen or paraffin-embedded material of other types of tumors with myxoid morphology (seven myxoid malignant fibrous histiocytomas and four lipomas with myxoid change). These results indicate that this molecular assay can be applied to formalin-fixed, paraffin-embedded tumor tissues as a diagnostic aid for these subtypes of liposarcoma.

It is well established that the majority of myxoid/round cell liposarcomas (LPS) are characterized by a reciprocal translocation t(12;16)(q13;p11) which at the molecular level results infusion of the CHOP and FUS/TLS genes. It is assumed that functional characterization of these genes may provide insight into the molecular pathogenesis of this tumour type. This study describes two new cases of myxoid/round cell LPS having a t(12;22). By reverse transcription-polymerase chain reaction (RT-PCR) it has been shown that this leads to fusion between the CHOP and EWS genes, thus indicating involvement of the EWS gene, at least occasionally, in yet another sarcoma type. Combining these two cases with two others which were recently similarly characterized at the molecular level, their clinicopathological features have been compared with cases having the more usual t(12;16). It was not possible to identify any clinical or pathological differences between these molecular genetic subsets. The relevance or significance of these gene fusion products in myxoid/round cell LPS remains to be determined.

Cytogenetic analysis of a short-term culture from a round cell liposarcoma revealed ins(12;16)(q13;p11.2p13) as a sole abnormality in all metaphase cells studied. This chromosome rearrangement, thus far not described in liposarcomas, leads to recombination of bands 12q13 and 16p11.2 and, thus, seems to be the equivalent of t(12;16)(q13;p11), a translocation that is highly specific for the myxoid type of liposarcoma. Our case represents the fourth fully karyotyped round cell liposarcoma that displays a cytogenetic rearrangement of bands 12q13 and 16p11, thus supporting the concept that round cell liposarcoma is related to myxoid liposarcoma and constitutes its poorly differentiated form. The fact that ins(12;16) was the only detectable chromosome aberration suggests that the presence of secondary cytogenetic aberrations is not a prerequisite for the development of a round cell histology in liposarcoma.

The cytogenetic analysis of a patient with a myxoid liposarcoma exhibiting cartilaginous differentiation is presented. A complex translocation involving chromosome 12, 16, and 19 was found, instead of the t(12;16), specific for myxoid liposarcoma. The involvement of 19q13 in a tumor with cartilaginous differentiation, and the assignment of TGF beta 1 to 19q13.1-13.2, which appears to play a role in the formation of bone and cartilage, suggest a possible relation between both.

Myxoid liposarcoma (MLS) is the most common subtype of liposarcoma. The cytogenetic hallmark of MLS is the pathognomonic t(12;16)(q13;p11), present in more than 85% of cases. The translocation leads to the fusion of the CHOP and FUS genes at 12q13 and 16p11, respectively, and the generation of a FUS/CHOP hybrid protein. The presence of a tumor-specific chimeric gene makes it possible to identify MLS cells by polymerase chain reaction (PCR). We have analyzed peripheral blood samples obtained during a 10-year period at diagnosis of primary and/or recurrent disease in 19 MLS patients with t(12;16) and in one MLS patient with t(12;22;20), resulting in the fusion of the CHOP and EWS genes. Nested PCR on genomic DNA from blood samples amplified FUS/CHOP hybrid fragments in three patients and EWS/CHOP in the patient with t(12;22;20). There was no obvious association between PCR findings and clinical outcome, but larger series are needed to draw any firm conclusions.

Cytogenetic analysis carried out in 28 adipose tissue tumors diagnosed microscopically as myxoid liposarcoma (ML) revealed a t(12;16)(q13:p11) chromosomal translocation in 26 of the 28 cases. Morphologically, these tumors were subclassified into the following categories: well-differentiated, six cases: poorly differentiated round cell type, 17 cases: poorly differentiated spindle cell type, five cases. Poorly differentiated ML behaved in a more aggressive fashion than the well-differentiated tumors. The results of this study confirm the consistency and specificity of the t(12;16)(q13:p11) translocation as the genetic marker of ML, support the contention that liposarcomas with round cells belong to the ML category, and confirm Stout's proposal for the existence of a poorly differentiated ML composed of spindle cells. Cytogenetic analysis may be helpful in the differential diagnosis of ML with atypical lipomatous tumors, which is characteristically associated with ring and giant marker chromosomes, and of ML with lipoblastoma, which is typically associated with 8q alterations. The existence of a mixed ML-atypical lipomatous tumor remains questionable. The genetic events associated with the greater aggressiveness of the poorly differentiated types of ML remain to be determined.

Analysis of chromosomal alterations in human malignancies has revealed recurring genetic changes that are often closely associated with specific subtypes of tumours. Among solid tumours, cytogenetic analysis of a group of primitive sarcomas occurring principally in children and young adults has identified specific non-random chromosomal translocations associated with these malignancies. A number of the translocation breakpoints have now been cloned, revealing the in frame fusion of genes located at each partner breakpoint. The common theme is the expression by these hybrid genes of chimaeric proteins containing functional domains from each fusion partner. These domains confer transcriptional activation or repression, DNA binding specificity, or other novel protein-protein interactions. The net result appears to be the expression of chimaeric oncoproteins that function in transformation by dysregulating gene transcription.

The translocation t(12;16)(q13;p11), which cytogenetically characterizes myxoid liposarcomas (MLS), results in a fusion of the CHOP gene in 12q13 and the FUS gene in 16p11, creating a chimeric FUS/CHOP gene. We have identified two cases of MLS with translocations giving rise to recombination between 12q13 and 22q12. The result was a fusion of the N-terminal part of the EWS gene in 22q12, involved in a number of mesenchymal tumor types, with the CHOP gene and the creation of an EWS/CHOP chimeric gene. The presence of the EWS/CHOP chimeric gene in MLS shows that (i) the N-terminal part of FUS may be replaced by the N-terminal part of EWS in a CHOP fusion oncoprotein (ii) the two N-terminal parts, when fused to certain transcription factors, have a common or very similar oncogenic potential and (iii) the tumorigenic process in MLS and the morphogenetically distinctly different EWS-associated tumor types may be related.

The FUS gene, which maps to 16p11, is fused to the CHOP gene in the t(12;16) (q13;p11) that characterizes myxoid liposarcomas (MLS) and to the ERG gene in acute myeloid leukemia (AML) with t(16;21) (p11;q22). In the present study we have mapped the breakpoints within FUS in 13 MLS with t(12;16) and in one AML with t(16;21). This region of FUS is about 3.9 kb and contains four exons. The breakpoints clustered to two zones (1 and 2). A strong association was found between the two known types of FUS/CHOP transcripts and the genomic localization of the breakpoints. In all cases expressing only type I or both type I and II FUS/CHOP transcript the genomic breakpoints mapped to zone 1. In all cases expressing only the type II transcript the breakpoints occurred in zone 2. The breakpoint in the AML case was in zone 1, suggesting that in-frame fusion transcripts are selected by similar mechanisms in both MLS and AML.

Translocation t(12;16)(q13;p11) is regarded as a diagnostic marker for myxoid liposarcoma. Cytogenetic data on round cell liposarcomas and combined myxoid and round cell tumors is scarce, and the genetic basis of progression of myxoid tumors to high grade, round cell lesions is unknown. We have accumulated six round cell, four combined myxoid and round cell, and three myxoid liposarcomas for analysis. t(12;16)(q13;p11) was present in three round cell lesions and was detectable in all of the tumors by DNA analysis. In each tumor type, the CHOP gene in 12q13 was rearranged and fused to the TLS gene in 16p11. A variant TLS-CHOP RNA transcript was detected by polymerase chain reaction but did not correlate with clinicopathological data. No distinguishing cytogenetic or molecular markers for round cell or mixed lesions were found. The histogenic and genetic relatedness of myxoid and round cell liposarcomas is apparent from these data.

Myxoid liposarcomas are cytogenetically characterized by t(12;16)(q13;p11). The translocation results in rearrangements of the CHOP gene in 12q13 and the FUS gene in 16p11, creating a fusion gene where the RNA-binding domain of FUS is replaced by the DNA-binding and leucine zipper dimerization domain of CHOP. In the present study, we have mapped 16 genomic breakpoints in the region of the CHOP gene and isolated and sequenced a new variant (type II) of the chimeric FUS/CHOP transcript. The genomic breakpoints were dispersed along a 7.50-kilobase pair region from a SstI cleavage site upstream of the promoter of CHOP to a PstI cleavage site within intron 1. Reverse transcriptase-polymerase chain reaction analysis of tumor samples demonstrated the presence of two variant fragments, 654 base pairs (type I) and 378 base pairs (type II) in size. Of the 13 samples analyzed, 7 showed the smaller, 3 showed the larger, and 3 showed both types of transcripts. We cloned and sequenced the two fragments and found in type II a novel fusion point in the FUS mRNA 275 base pairs upstream of that present in the type I transcript. In both types of transcripts the interrupted FUS is followed by the entire exon 2 of CHOP. As a consequence the normally nontranslated exon 2 is translated and in both types there is in the junction between FUS and CHOP a shift from a FUS glycine codon to a valine codon in the chimeric mRNA.

The consistent involvement of the region 12q13-q15 in numerous human tumors speaks in favor of the presence of genes that may contribute to oncogenesis. Mapping genes within this region of chromosome 12 is a necessary step toward the identification of those that play a role in this process. We have undertaken a multiplex analysis using translocation breakpoint mapping to order from the centromere to the telomere a series of 24 loci from the region 12q12-q22. Thirteen adipose tissue tumors with seven different chromosome changes involving the long arm of chromosome 12 (12q) were used. Since most of these loci are genes or anonymous DNA segments largely available to the scientific community, this map should be useful for investigation of genetic disorders associated with chromosome 12q. While these breakpoints were used as natural landmarks to order groups of loci, this work has positioned them more accurately, leading to a better chromosomal definition of the translocations than the one derived from standard cytogenetic studies.

Many sarcomas contain characteristic chromosome translocations that result in the fusion of genes from two different chromosomes. This review focuses on the translocated genes that have been identified recently in Ewing's sarcoma, peripheral primitive neuroectodermal tumor, clear cell sarcoma, alveolar rhabdomyosarcoma, and myxoid liposarcoma. Each of these fusion genes encodes a DNA transcription factor that presumably regulates the function of other genes. Thus, a common mechanism of oncogenesis has been defined in histologically disparate varieties of sarcoma.

The t(16;21)(p11;q22) translocation is a recurrent chromosomal abnormality found in several types of myeloid leukemia. We have previously demonstrated that the breakpoints of this translocation are clustered in a specific intron of the ERG gene on chromosome 21, which has recently been reported to be involved in Ewing's sarcoma. We show here that the TLS/FUS gene on chromosome 16 is fused with the ERG gene to produce the TLS/FUS-ERG chimeric transcript by this translocation. The TLS/FUS gene has been identified as a translocated gene in myxoid liposarcoma by the t(12;16)(q13;p11) translocation and encodes an RNA-binding protein that is highly homologous to the product of the EWS gene involved in Ewing's sarcoma. Thus, the TLS/FUS-ERG gene fusion in t(16;21) leukemia is predicted to produce a protein that is very similar to the EWS-ERG chimeric protein responsible for Ewing's sarcoma.