Structural analysis of PAX3 genomic rearrangements in alveolar rhabdomyosarcoma

Expression of oncogenic HRAS in human Rh28 and RMS-YM rhabdomyosarcoma cells leads to oncogene-induced senescence

Rhabdomyosarcoma (RMS) is the most common pediatric soft tissue sarcoma. The two predominant histologic variants of RMS, embryonal and alveolar rhabdomyosarcoma (eRMS and aRMS, respectively), carry very different prognoses. While eRMS is associated with an intermediate prognosis, the 5-year survival rate of aRMS is less than 30%. The RMS subtypes are also different at the molecular level-eRMS frequently has multiple genetic alterations, including mutations in RAS and TP53, whereas aRMS often has chromosomal translocations resulting in PAX3-FOXO1 or PAX7-FOXO1 fusions, but otherwise has a "quiet" genome. Interestingly, mutations in RAS are rarely found in aRMS. In this study, we explored the role of oncogenic RAS in aRMS. We found that while ectopic oncogenic HRAS expression was tolerated in the human RAS-driven eRMS cell line RD, it was detrimental to cell growth and proliferation in the human aRMS cell line Rh28. Growth inhibition was mediated by oncogene-induced senescence and associated with increased RB pathway activity and expression of the cyclin-dependent kinase inhibitors p16 and p21. Unexpectedly, the human eRMS cell line RMS-YM, a RAS wild-type eRMS cell line, also exhibited growth inhibition in response to oncogenic HRAS in a manner similar to aRMS Rh28 cells. This work suggests that oncogenic RAS is expressed in a context-dependent manner in RMS and may provide insight into the differential origins and therapeutic opportunities for RMS subtypes.

Sarcoma Subgrouping by Detection of Fusion Transcripts Using NanoString nCounter Technology

BACKGROUND

NanoString technology is an innovative barcode-based system that requires less tissue than traditional techniques and can test for multiple fusion transcripts in a single reaction. The objective of this study was to determine the utility of NanoString technology in the detection of sarcoma-specific fusion transcripts in pediatric sarcomas.

DESIGN

Probe pairs for the most common pediatric sarcoma fusion transcripts were designed for the assay. The NanoString assay was used to test 22 specific fusion transcripts in 45 sarcoma samples that had exhibited one of these fusion genes previously by reverse transcription polymerase chain reaction (RT-PCR). A mixture of frozen (n = 18), formalin-fixed, paraffin-embedded (FFPE) tissue (n = 23), and rapid extract template (n = 4) were used for testing.

RESULTS

Each of the 22 transcripts tested was detected in at least one of the 45 tumor samples. The results of the NanoString assay were 100% concordant with the previous RT-PCR results for the tumor samples, and the technique was successful using both FFPE and rapid extract method.

CONCLUSION

Multiplexed interrogation for sarcoma-specific fusion transcripts using NanoString technology is a reliable approach for molecular diagnosis of pediatric sarcomas and works well with FFPE tissues. Future work will involve validating additional sarcoma fusion transcripts as well as determining the optimal workflow for diagnostic purposes.

The expression and function of PAX3 in development and disease

The PAX3 gene encodes a member of the PAX family of transcription factors that is characterized by a highly conserved paired box motif. The PAX3 protein is a transcription factor consisting of an N-terminal DNA binding domain (containing a paired box and homeodomain) and a C-terminal transcriptional activation domain. This protein is expressed during development of skeletal muscle, central nervous system and neural crest derivatives, and regulates expression of target genes that impact on proliferation, survival, differentiation and motility in these lineages. Germline mutations of the murine Pax3 and human PAX3 genes cause deficiencies in these developmental lineages and result in the Splotch phenotype and Waardenburg syndrome, respectively. Somatic genetic rearrangements that juxtapose the PAX3 DNA binding domain to the transcriptional activation domain of other transcription factors deregulate PAX3 function and contribute to the pathogenesis of the soft tissue cancers alveolar rhabdomyosarcoma and biphenotypic sinonasal sarcoma. The wild-type PAX3 protein is also expressed in other cancers related to developmental lineages that normally express this protein and exerts phenotypic effects related to its normal developmental role.

Secreted Frizzled-Related Protein 3 (SFRP3) Is Required for Tumorigenesis of PAX3-FOXO1-Positive Alveolar Rhabdomyosarcoma

PURPOSE

Rhabdomyosarcoma (RMS) is a soft tissue sarcoma associated with the skeletal muscle lineage. Of the two predominant subtypes, known as embryonal (eRMS) and alveolar (aRMS), aRMS has the poorer prognosis, with a five-year survival rate of <50%. The majority of aRMS tumors express the fusion protein PAX3-FOXO1. As PAX3-FOXO1 has proven chemically intractable, this study aims to identify targetable proteins that are downstream from or cooperate with PAX3-FOXO1 to support tumorigenesis.

EXPERIMENTAL DESIGN

Microarray analysis of the transcriptomes of human skeletal muscle myoblasts expressing PAX3-FOXO1 revealed alteration of several Wnt pathway gene members, including secreted frizzled related protein 3 (SFRP3), a secreted Wnt pathway inhibitor. Loss-of-function using shRNAs against SFRP3 was used to interrogate the role of SFRP3 in human aRMS cell lines in vitro and conditional murine xenograft systems in vivo. The combination of SFRP3 genetic suppression and the chemotherapeutic agent vincristine was also examined.

RESULTS

In vitro, suppression of SFRP3 inhibited aRMS cell growth, reduced proliferation accompanied by a G1 arrest and induction of p21, and induced apoptosis. In vivo, doxycycline-inducible suppression of SFRP3 reduced aRMS tumor growth and weight by more than three-fold, in addition to increasing myogenic differentiation and β-catenin signaling. The combination of SFRP3 suppression and vincristine was more effective at reducing aRMS cell growth in vitro than either treatment alone, and ablated tumorigenesis in vivo.

CONCLUSIONS

SFRP3 is necessary for the growth of human aRMS cells both in vitro and in vivo and is a promising new target for investigation in aRMS.

Classification of rhabdomyosarcoma and its molecular basis

Rhabdomyosarcoma (RMS), the most common soft tissue sarcoma in children, has traditionally been classified into embryonal rhabdomyosarcoma (ERMS) and alveolar rhabdomyosarcoma (ARMS) for pediatric oncology practice. This review outlines the historical development of classification of childhood RMS and the challenges that have been associated with it, particularly problems with the diagnosis of "solid variant" ARMS and its distinction from ERMS. In addition to differences in clinical presentation and outcome, a number of genetic features underpin separation of ERMS from ARMS. Genetic differences associated with RMS subclassification include the presence of reciprocal translocations and their associated fusions in ARMS, amplification of genes in ARMS and its fusion subsets, chromosomal losses and gains that mostly occur in ERMS, and allelic losses and mutations usually associated with ERMS. Chimeric proteins encoded in most ARMS from the fusion of PAX3 or PAX7 with FOXO1 are expressed, result in a distinct pattern of downstream protein expression, and appear to be the proximate cause of the bad outcome associated with this subtype. A sizeable minority of ARMS lacks these fusions and shares the clinical and biological features of ERMS. A battery of immunohistochemical tests may prove useful in separating ERMS from ARMS and fusion-positive ARMS from fusion-negative ARMS. Because of limitation of predicting outcome solely based on histologic classification, treatment protocols will begin to utilize fusion testing for stratification of affected patients into low-risk, intermediate-risk, and high-risk groups.

Human rhabdomyosarcoma cell lines for rhabdomyosarcoma research: utility and pitfalls

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood and adolescence. Despite intergroup clinical trials conducted in Europe and North America, outcomes for high risk patients with this disease have not significantly improved in the last several decades, and survival of metastatic or relapsed disease remains extremely poor. Accrual into new clinical trials is slow and difficult, so in vitro cell-line research and in vivo xenograft models present an attractive alternative for preclinical research for this cancer type. Currently, 30 commonly used human RMS cell lines exist, with differing origins, karyotypes, histologies, and methods of validation. Selecting an appropriate cell line for RMS research has important implications for outcomes. There are also potential pitfalls in using certain cell lines including contamination with murine stromal cells, cross-contamination between cell lines, discordance between the cell line and its associated original tumor, imposter cell lines, and nomenclature errors that result in the circulation of two or more presumed unique cell lines that are actually from the same origin. These pitfalls can be avoided by testing for species-specific isoenzymes, microarray analysis, assays for subtype-specific fusion products, and short tandem repeat analysis.

Structural and functional studies of FKHR-PAX3, a reciprocal fusion gene of the t(2;13) chromosomal translocation in alveolar rhabdomyosarcoma

Alveolar rhabdomyosarcoma (ARMS) is an aggressive pediatric cancer of skeletal muscle. More than 70% of ARMS tumors carry balanced t(2;13) chromosomal translocation that leads to the production of two novel fusion genes, PAX3-FKHR and FKHR-PAX3. While the PAX3-FKHR gene has been intensely studied, the reciprocal FKHR-PAX3 gene has rarely been described. We report here the cloning and functional characterization of the FKHR-PAX3 gene as the first step towards a better understanding of its potential impact on ARMS biology. From RH30 ARMS cells, we detected and isolated three versions of FKHR-PAX3 cDNAs whose C-terminal sequences corresponded to PAX3c, PAX3d, and PAX3e isoforms. Unlike the nuclear-specific localization of PAX3-FKHR, the reciprocal FKHR-PAX3 proteins stayed predominantly in the cytoplasm. FKHR-PAX3 potently inhibited myogenesis in both non-transformed myoblast cells and ARMS cells. We showed that FKHR-PAX3 was not a classic oncogene but could act as a facilitator in oncogenic pathways by stabilizing PAX3-FKHR expression, enhancing cell proliferation, clonogenicity, anchorage-independent growth, and matrix adhesion in vitro, and accelerating the onset of tumor formation in xenograft mouse model in vivo. In addition to these pro-oncogenic behaviors, FKHR-PAX3 also negatively affected cell migration and invasion in vitro and lung metastasis in vivo. Taken together, these functional characteristics suggested that FKHR-PAX3 might have a critical role in the early stage of ARMS development.

FGFR4 blockade exerts distinct antitumorigenic effects in human embryonal versus alveolar rhabdomyosarcoma

PURPOSE

Rhabdomyosarcoma (RMS) is a malignancy with features of skeletal muscle, and the most common soft tissue sarcoma of childhood. Survival for high-risk groups is approximately 30% at 5 years and there are no durable therapies tailored to its genetic aberrations. During genetic modeling of the common RMS variants, embryonal RMS (eRMS) and alveolar RMS (aRMS), we noted that the receptor tyrosine kinase (RTK) fibroblast growth factor receptor 4 (FGFR4) was upregulated as an early event in aRMS. Herein, we evaluated the expression of FGFR4 in eRMS compared with aRMS, and whether FGFR4 had similar or distinct roles in their tumorigenesis.

EXPERIMENTAL DESIGN

Human RMS cell lines and tumor tissue were analyzed for FGFR4 expression by immunoblot and immunohistochemistry. Genetic and pharmacologic loss-of-function of FGFR4 using virally transduced short hairpin RNA (shRNA) and the FGFR small-molecule inhibitor PD173074, respectively, were used to study the role of FGFR4 in RMS cell lines in vitro and xenografts in vivo. Expression of the antiapoptotic protein BCL2L1 was also examined.

RESULTS

FGFR4 is expressed in both RMS subtypes, but protein expression is higher in aRMS. The signature aRMS gene fusion product, PAX3-FOXO1, induced FGFR4 expression in primary human myoblasts. In eRMS, FGFR4 loss-of-function reduced cell proliferation in vitro and xenograft formation in vivo. In aRMS, it diminished cell survival in vitro. In myoblasts and aRMS, FGFR4 was necessary and sufficient for expression of BCL2L1 whereas in eRMS, this induction was not observed, suggesting differential FGFR4 signaling.

CONCLUSION

These studies define dichotomous roles for FGFR4 in RMS subtypes, and support further study of FGFR4 as a therapeutic target.

Targeted therapy in bone and soft tissue sarcoma in children and adolescents

Pediatric soft-tissue and bone sarcomas are a heterogeneous group of tumors of mesenchymal origin which affect approximately 1,500 children in the United States each year. Using multimodal therapy (surgery, radiation, and chemotherapy),the overall 5-year survival rate for children with soft-tissue and bone sarcomas is approximately 60%–70%. However, the prognosis for children with metastatic or recurrent disease is poor; and, furthermore, the improvements in the overall cure rate have slowed. It is highly unlikely that further advances in the treatment of pediatric soft-tissue and bone sarcomas will come from traditional cytotoxic chemotherapy. Based on research advances in understanding the biology of pediatric soft-tissue and bone sarcomas, improved cure rates will likely be driven by new types of treatment which target the specific abnormalities within these tumors. These new targeted therapies may include small molecules, antibodies, or other immunotherapies. This review briefly describes the biology of the major types of pediatric sarcomas, discusses potential targets for new therapy, and highlights some recent and current clinical trials using targeted therapy.

Childhood rhabdomyosarcoma: recent advances and prospective views

Rhabdomyosarcoma (RMS) is a morphologically and clinically heterogeneous group of malignant tumors that resemble developing skeletal muscle and is the most common soft-tissue sarcoma in children and adolescents. The most prominent sites involve head and neck structures (~40%), genito-urinary track (~25%), and extremities (~20%). Embryonal (ERMS) and alveolar (ARMS) are the two major RMS subtypes that are distinct in their morphology and genetic make-up. The prognosis for this cancer depends strongly on tumor size, location, staging, and child's age. In general, ERMS has a more favorable outcome, whereas the mortality rate remains high in patients with ARMS, because of its aggressive and metastatic nature. Over the past two decades, researchers have made concerted efforts to delineate genetic and epigenetic changes associated with RMS pathogenesis. These molecular signatures have presented golden opportunities to design targeted therapies for treating this aggressive cancer. This article highlights recent advances in understanding the molecular pathogenesis of RMS, and addresses promising research areas for further exploration.

Myogenesis and rhabdomyosarcoma the Jekyll and Hyde of skeletal muscle

Rhabdomyosarcoma, a neoplasm composed of skeletal myoblast-like cells, represents the most common soft tissue sarcoma in children. The application of intensive chemotherapeutics and refined surgical and radiation therapy approaches have improved survival for children with localized disease over the past 3 decades; however, these approaches have not improved the dismal outcome for children with metastatic and recurrent rhabdomyosarcoma. Elegant studies have defined the molecular mechanisms driving skeletal muscle lineage commitment and differentiation, and the machinery that couples differentiation with irreversible cell proliferation arrest. Further, detailed molecular analyses indicate that rhabdomyosarcoma cells have lost the capacity to fully differentiate when challenged to do so in experimental models. We review the intersection of normal skeletal muscle developmental biology and the molecular genetic defects in rhabdomyosarcoma with the underlying premise that understanding how the differentiation process has gone awry will lead to new treatment strategies aimed at promoting myogenic differentiation and concomitant cell cycle arrest.

Pigmentation PAX-ways: the role of Pax3 in melanogenesis, melanocyte stem cell maintenance, and disease

Transcription factors initiate programs of gene expression and are catalysts in downstream molecular cascades that modulate a variety of cellular processes. Pax3 is a transcription factor that is important in the melanocyte and influences melanocytic proliferation, resistance to apoptosis, migration, lineage specificity and differentiation. In this review, we focus on Pax3 and the molecular pathways that Pax3 is a part of during melanogenesis and in the melanocyte stem cell. These roles of Pax3 are emphasized during the development of diseases and syndromes resulting from either too much or too little Pax3 function. Due to its key task in melanocyte stem cells and tumors, the Pax3 pathway may provide an ideal target for either stem cell or cancer therapies.

Embryonal and alveolar rhabdomyosarcoma of parameningeal sites in adults: a report of 13 cases

This study reports 13 adult parameningeal rhabdomyosarcomas. Ages ranged from 18 to 86 years. Nine lesions were alveolar, 3 were embryonal, and 1 could not be further classified. All cases were positive for desmin and/or myogenin and 1 tumor was strongly positive for cytokeratin. PAX3-FKHR or PAX7-FKHR fusion transcripts or FKHR breaks were identified in 5 cases confirming a diagnosis of alveolar rhabdomyosarcoma. Three cases were negative supporting a diagnosis of embryonal rhabdomyosarcoma. A total of 10 patients were treated with chemotherapy and radiation. Three patients are alive with no disease, 3 are alive with disease, 3 died of disease, and 4 patients are lost to follow-up. Adult sinonasal rhabdomyosarcoma is uncommon and should be considered in the differential of sinonasal neoplasms. Disease can occur in the elderly. Desmin and myogenin can aid in the diagnosis but cytokeratin reactivity can be seen and care must be taken not to diagnose carcinoma.

Validation of met as a therapeutic target in alveolar and embryonal rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a highly malignant soft-tissue tumor of childhood deriving from skeletal muscle cells. RMS can be classified in two major histologic subtypes: embryonal (ERMS) and alveolar (ARMS), the latter being characterized by the PAX3/7-FKHR translocation. Here we first investigated whether the Met receptor, a transcriptional target of PAX3 and PAX7, has a role in PAX3-FKHR-mediated transformation. Following PAX3-FKHR transduction, Met was up-regulated in mouse embryonal fibroblasts (MEF), NIH 3T3 and C2C12 cells, and they all acquired anchorage independence. This property was lost in low serum but addition of hepatocyte growth factor/scatter factor (HGF/SF) rescued soft-agar growth. Genetic proof that Met is necessary for this PAX3-FKHR-mediated effect was obtained by transducing with PAX3-FKHR MEFs derived from Met mutant (Met(D/D)) and wild-type (Met(+/+)) embryos. Only Met(+/+) MEFs acquired anchorage-independent growth whereas PAX3-FKHR-transduced Met(D/D) cells were unable to form colonies in soft agar. To verify if Met had a role in RMS maintenance, we silenced the receptor by transducing ERMS and ARMS cell lines with an inducible lentivirus expressing an anti-Met short hairpin RNA (shRNA). Met down-regulation significantly affected RMS cells proliferation, survival, invasiveness, and anchorage-independent growth. Finally, induction of the Met-directed shRNA promoted a dramatic reduction of tumor mass in a xenograft model of RMS. Our data show that both ARMS- and ERMS-derived cell lines, in spite of the genetic drift which may have occurred in years of culture, seem to have retained an "addiction" to the Met oncogene and suggest that Met may represent a target of choice to develop novel therapeutic strategies for ARMS.

Characteristic sequence motifs located at the genomic breakpoints of the translocation t(X;18) in synovial sarcomas

The SYT-SSXI and SYT-SSX2 fusion genes, derived by reciprocal translocations t(X;18), are acquired genetic events strongly associated with the tumorigenesis of synovial sarcoma. In approaching the mechanisms underlying the formation of these fusion oncogenes, we have analysed the genomic sequences surrounding the SYT-SSX breakpoints in 10 tumors, two expressing SYT-SSXI and eight expressing SYT-SSX2 fusion transcripts. The breakpoints were found to be clustered in the 5' end of intron 10 of SYT, and in two cluster regions within intron 4 of SSX2, whereas the two breakpoints in SSX1 intron 4 were 0.5 kb apart. SYT intron 10 is abundant in repetitive regions with the interspersed repeats occupying 66% of the whole intron. Nine of the 10 breakpoints in intron 10 of SYT and six of the eight breakpoints in intron 4 of SSX2 were at or near repetitive regions. These findings suggest that repetitive regions may contribute to the distribution of genomic breakpoints. Several of the fusion sequences exhibited characteristic signs of nonhomologous end joining, including microhomologies at the end points as well as deletions. Sequences highly homologous (83-94%) to consensus topoisomerase II cleavage sites were identified at or near the breakpoints in all 10 tumors, suggesting a role of this enzyme in creating staggered ends at the breakpoint. Furthermore, sequences highly homologous to consensus Translin binding sequences were found at the breakpoints in two cases, and an Alu-Alu fusion and an insertion of a 206-bp LINE-1 element were found at the breakpoint in one case each. The demonstration of characteristic sequences at the SYT-SSX breakpoint regions is expected to improve our understanding of the molecular genetic mechanisms behind translocations in general, and of the SYT-SSX fusions in synovial sarcoma in particular.

Use of inverse PCR to amplify and sequence breakpoints of HPRT deletion and translocation mutations

Deletion and translocation mutations have been shown to play a significant role in the genesis of many cancers. The hprt gene located at Xq26 is a frequently used marker gene in human mutational studies. In an attempt to better understand potential mutational mechanisms involved in deletions and translocations, inverse PCR (IPCR) methods to amplify and sequence the breakpoints of hprt mutants classified as translocations and large deletions were developed. IPCR involves the digestion of DNA with a restriction enzyme, circularization of the fragments produced, and PCR amplification around the circle with primers oriented in a direction opposite to that of conventional PCR. The use of this technique allows amplification into an unknown region, in this case through the hprt breakpoint into the unknown joined sequence. Through the use of this procedure, two translocation, one inversion, and two external deletion hprt breakpoint sequences were isolated and sequenced. The isolated IPCR products range in size from 0.4 to 1.8 kb, and were amplified from circles ranging in size from 0.6 to 7.7 kb. We have shown that inverse PCR is useful to sequence translocation and large deletion mutant breakpoints in the hprt gene.

Gene fusions involving PAX and FOX family members in alveolar rhabdomyosarcoma

The chromosomal translocations t(2;13)(q35;q14) and t(1;13)(p36;q14) are characteristic of alveolar rhabdomyosarcoma, a pediatric soft tissue cancer related to the striated muscle lineage. These translocations rearrange PAX3 and PAX7, members of the paired box transcription factor family, and juxtapose these genes with FKHR, a member of the fork head transcription factor family. This juxtaposition generates PAX3-FKHR and PAX7-FKHR chimeric genes that are expressed as chimeric transcripts that encode chimeric proteins. The fusion proteins, which contain the PAX3/PAX7 DNA binding domain and the FKHR transcriptional activation domain, activate transcription from PAX-binding sites with higher potency than the corresponding wild-type PAX proteins. This increased function results from the insensitivity of the FKHR activation domain to inhibitory effects of N-terminal PAX3/PAX7 domains. In addition to altered function, the fusion products are expressed in ARMS tumors at higher levels than the corresponding wild-type PAX products due to two distinct mechanisms. The PAX7-FKHR fusion is overexpressed as a result of in vivo amplification while the PAX3-FKHR fusion is overexpressed due to a copy number-independent increase in transcriptional rate. Finally, though FKHR subcellular localization is regulated by an AKT-dependent pathway, the fusion proteins are resistant to these signals and show exclusively nuclear localization. Therefore, these translocations alter biological activity at the levels of protein function, gene expression, and subcellular localization with the cumulative outcome postulated to be aberrant regulation of PAX3/PAX7 target genes. This aberrant gene expression program is then hypothesized to contribute to tumorigenic behavior by impacting on the control of growth, apoptosis, differentiation and motility.

Molecular features of a human rhabdomyosarcoma cell line with spontaneous metastatic progression

A novel human cell line was established from a primary botryoid rhabdomyosarcoma. Reverse transcription polymerase chain reaction investigations of this cell line, called RUCH-2, demonstrated expression of the regulatory factors PAX3, Myf3 and Myf5. After 3.5 months in culture, cells underwent a crisis after which Myf3 and Myf5 could no longer be detected, whereas PAX3 expression remained constant over the entire period. Karyotype analysis revealed breakpoints in regions similar to previously described alterations in primary rhabdomyosarcoma tumour samples. Interestingly, cells progressed to a metastatic phenotype, as observed by enhanced invasiveness in vitro and tumour growth in nude mice in vivo. On the molecular level, microarray analysis before and after progression identified extensive changes in the composition of the extracellular matrix. As expected, down-regulation of tissue inhibitors of metalloproteinases and up-regulation of matrix metalloproteinases were observed. Extensive down-regulation of several death receptors of the tumour necrosis factor family suggests that these cells might have an altered response to appropriate apoptotic stimuli. The RUCH-2 cell line represents a cellular model to study multistep tumorigenesis in human rhabdomyosarcoma, allowing molecular comparison of tumorigenic versus metastatic cancer cells.

Structural analysis of PAX7 rearrangements in alveolar rhabdomyosarcoma

In the pediatric cancer alveolar rhabdomyosarcoma, the common 2;13 and less frequent 1;13 translocations fuse PAX3 and PAX7, respectively, with FKHR to produce chimeric genes. To compare structural features of these rearrangements, we cloned and mapped a 64-kb genomic region containing PAX7 exons 5 through 8. With the use of Southern blot methodology, rearrangements of the 30-kb PAX7 intron 7 were detected in 9 of 9 PAX7-FKHR-positive cases. Similar to our t(2;13) studies, the t(1;13) breakpoints were randomly distributed within the seventh intron. In contrast with the > 90% frequency of reciprocal rearrangements in the t(2;13), reciprocal rearrangements involving the 3' PAX7 region were detected in only 4 of 9 cases. Furthermore, we detected PAX7-FKHR genomic amplification in 10 of 11 cases, in contrast with the < 5% frequency of PAX3-FKHR amplification. The differences in occurrence, reciprocity, and amplification between the PAX3-FKHR and PAX7-FKHR fusions indicate important differences in the mechanism of the two associated chromosomal translocation events.

Osteosarcoma associated with absent thumbs: a report of two cases

An 8-year-old Hispanic boy with a hypoplastic left thumb, absent right thumb, and short stature experienced right leg pain and limp. A right tibial lesion was imaged and found to be osteosarcoma on biopsy. A 6-year-old Hispanic girl with congenitally absent thumbs experienced a pathologic fracture of her left femur after a minor sports injury. The radiologic abnormality seen was diagnosed as osteosarcoma on biopsy. Both patients continue to do well after intensive preoperative and postoperative high-dose chemotherapy and definitive reconstructive limb surgery. Osteosarcoma has been linked to several congenital syndromes in which absent thumbs are a feature. These two patients with absent thumbs and no definable syndrome experiencing osteosarcoma suggest that congenitally absent thumbs might be a risk factor for osteosarcoma in the absence of a syndrome.

Genetics and the biologic basis of sarcomas

Identification of genetic alterations has contributed greatly to the understanding of sarcoma biology. Additionally, detection of these abnormalities is providing new tools for the diagnosis of sarcomas. In this paper, three important new genetic findings from the past year are reviewed, including the t(12;15) translocation of congenital fibrosarcoma, mutation of the putative tumor suppressor gene hSNF5/INI1 in malignant rhabdoid tumor, and the association of c-kit mutations with gastrointestinal stromal tumor. Highlighted are important studies concerning mechanisms of chromosomal translocation, functions of sarcoma-specific fusion proteins, genetic abnormalities other than translocations, molecular diagnosis, and molecular profiling of gene expression. Particular emphasis is placed on information obtained with comparative genomic hybridization and microarray techniques, because these powerful technologies will facilitate the rapid acquisition of data that provide insight into the molecular genetic and biologic basis of sarcomas.