Ewing family tumors: potential prognostic value of reverse-transcriptase polymerase chain reaction detection of minimal residual disease in peripheral blood samples

A comprehensive overview of liquid biopsy applications in pediatric solid tumors

Liquid biopsies are emerging as an alternative source for pediatric cancer biomarkers with potential applications during all stages of patient care, from diagnosis to long-term follow-up. While developments within this field are reported, these mainly focus on dedicated items such as a specific liquid biopsy matrix, analyte, and/or single tumor type. To the best of our knowledge, a comprehensive overview is lacking. Here, we review the current state of liquid biopsy research for the most common non-central nervous system pediatric solid tumors. These include neuroblastoma, renal tumors, germ cell tumors, osteosarcoma, Ewing sarcoma, rhabdomyosarcoma and other soft tissue sarcomas, and liver tumors. Within this selection, we discuss the most important or recent studies involving liquid biopsy-based biomarkers, anticipated clinical applications, and the current challenges for success. Furthermore, we provide an overview of liquid biopsy-based biomarker publication output for each tumor type based on a comprehensive literature search between 1989 and 2023. Per study identified, we list the relevant liquid biopsy-based biomarkers, matrices (e.g., peripheral blood, bone marrow, or cerebrospinal fluid), analytes (e.g., circulating cell-free and tumor DNA, microRNAs, and circulating tumor cells), methods (e.g., digital droplet PCR and next-generation sequencing), the involved pediatric patient cohort, and proposed applications. As such, we identified 344 unique publications. Taken together, while the liquid biopsy field in pediatric oncology is still behind adult oncology, potentially relevant publications have increased over the last decade. Importantly, steps towards clinical implementation are rapidly gaining ground, notably through validation of liquid biopsy-based biomarkers in pediatric clinical trials.

Ewing Sarcoma-Diagnosis, Treatment, Clinical Challenges and Future Perspectives

Ewing sarcoma, a highly aggressive bone and soft-tissue cancer, is considered a prime example of the paradigms of a translocation-positive sarcoma: a genetically rather simple disease with a specific and neomorphic-potential therapeutic target, whose oncogenic role was irrefutably defined decades ago. This is a disease that by definition has micrometastatic disease at diagnosis and a dismal prognosis for patients with macrometastatic or recurrent disease. International collaborations have defined the current standard of care in prospective studies, delivering multiple cycles of systemic therapy combined with local treatment; both are associated with significant morbidity that may result in strong psychological and physical burden for survivors. Nevertheless, the combination of non-directed chemotherapeutics and ever-evolving local modalities nowadays achieve a realistic chance of cure for the majority of patients with Ewing sarcoma. In this review, we focus on the current standard of diagnosis and treatment while attempting to answer some of the most pressing questions in clinical practice. In addition, this review provides scientific answers to clinical phenomena and occasionally defines the resulting translational studies needed to overcome the hurdle of treatment-associated morbidities and, most importantly, non-survival.

The new horizon of liquid biopsy in sarcoma: the potential utility of circulating tumor nucleic acids

The diagnosis, treatment and prognosis of sarcoma are mainly dependent on tissue biopsy, which is limited in its ability to provide a panoramic view into the dynamics of tumor progression. In addition, effective biomarkers to monitor the progression and therapeutic response of sarcoma are lacking. Liquid biopsy, a recent technological breakthrough, has gained great attention in the last few decades. Nucleic acids (such as DNA, mRNAs, microRNAs, and long non-coding RNAs) that are released from tumors circulate in the blood of cancer patients and can be evaluated through liquid biopsy. Circulating tumor nucleic acids reflect the intertumoral and intratumoral heterogeneity, and thus liquid biopsy provides a noninvasive strategy to examine these molecules compared with traditional tissue biopsy. Over the past decade, a great deal of information on the potential utilization of circulating tumor nucleic acids in sarcoma screening, prognosis and therapy efficacy monitoring has emerged. Several specific gene mutations in sarcoma can be detected in peripheral blood samples from patients and can be found in circulating tumor DNA to monitor sarcoma. In addition, circulating tumor non-coding RNA may also be a promising biomarker in sarcoma. In this review, we discuss the clinical application of circulating tumor nucleic acids as blood-borne biomarkers in sarcoma.

Precision medicine approaches for the management of Ewing sarcoma: current perspectives

Advancements in molecular and genetic techniques have significantly furthered our biological understanding of Ewing sarcoma (ES). ES is typified by a driving TET-ETS fusion with an otherwise relatively quiet genome. Detection of one of several characteristic fusions, most commonly EWSR1-FLI1, is the gold standard for diagnosis. We discuss the current role of precision medicine in the diagnosis, treatment, and monitoring of ES. Continued efforts toward molecularly guided approaches are actively being pursued in ES to better refine prognosis, identify germline markers of disease susceptibility, influence therapeutic selection, effectively monitor disease activity in real time, and identify genetic and immunotherapeutic targets for therapeutic development.

Application of liquid biopsy in bone and soft tissue sarcomas: Present and future

Bone and soft tissue sarcomas account for approximately 1% of adult solid malignancies and 20% of pediatric solid malignancies. Sarcomas are divided into more than 50 subtypes. Each subtype is highly heterogeneous and characterized by significant morphological and phenotypic variability. Currently, sarcoma characterization is based on tissue biopsies. However, primary and invasive tissue biopsies may not accurately reflect the current disease condition following treatment as is may cause marked changes to the tumor cells. Liquid biopsy offers an alternative minimally invasive approach to provide dynamic tumor information, allowing for the application of precision medicine in the treatment of sarcomas. Recently, there have been numerous blood-based tumor components identified by liquid biopsy in sarcomas, including circulating tumor cells, circulating cell-free nucleic acids, tumor-derived exosomes and metabolites in circulation. Here, we summarize the current evolving technologies and then elaborate on emerging novel concepts that may further propel the field of liquid biopsy in sarcomas. We address the applications in the context of our current knowledge about liquid biopsy in sarcomas and highlight the potential of translating these recent advances into the clinic for more effective management strategies for sarcoma patients.

PCR-based amplification of circulating RNAs as prognostic and predictive biomarkers - Focus on neuroblastoma

Metastatic disease is a major challenge for cancer cure, haematogenous spread and subsequent growth of tumour cells at distant sites being the cause of most cancer deaths. Molecular characterization and detection of the tumour cells responsible for haematogenous spread may increase understanding of the biology of metastasis, help improve patient management and allow evaluation of novel treatments to prevent and eradicate this disease. The bone marrow is a common site to which tumour cells metastasize, from which they may re-circulate to other organs with a favourable microenvironment for growth. The detection of tumour cells in blood suggests one route for metastasis, and provides an accessible, minimally invasive liquid sample through which it may be possible to monitor and detect minimal disease and early signs of metastasis. Significant improvements in the sensitivity and specificity of tumour cell detection have been made, such that it is now possible to unambiguously detect a single tumour cell in over 10 million normal cells. However, the clinical impact of such low level disease and how to interpret the natural variation that can arise from sequential sampling of bone marrow aspirates and blood is currently largely unknown. This commentary will focus on the technical advancements and application of reverse transcriptase polymerase chain reaction to detect cancer mRNAs in bone marrow and blood, and discuss the potential clinical impact of this test in neuroblastoma.

Management of Ewing sarcoma family of tumors: Current scenario and unmet need

Ewing sarcoma family tumors (ESFT) are heterogeneous, aggressive group of disease with peak incidence in adolescent and young adults. The outcome has been improved dramatically from 10% with surgery and radiotherapy alone to 65%-70% now, in localized disease, with the introduction of chemotherapy. Chemotherapy regimen evolved from single agent to multiagent with effort of many cooperative clinical trials over decades. The usual treatment protocol include introduction of multi-agent chemotherapy in neoadjuvant setting to eradicate systemic disease with timely incorporation of surgery and/or radiotherapy as local treatment modality and further adjuvant chemotherapy to prevent recurrence. Risk adapted chemotherapy in neoadjuvant and adjuvant setting along with radiotherapy has been used in many international collaborative trials and has resulted in improved outcome, more so in patients with localized disease. The role of high dose chemotherapy with stem cell rescue is still debatable. The outcome of patients with metastatic disease is dismal with long term outcome ranges from 20%-40% depending on the sites of metastasis and intensity of treatment. There is a huge unmet need to improve outcome further, more so in metastatic setting. Novel therapy targeting the molecular pathways and pathogenesis of ESFT is very much required. Here we have discussed the current standard of management in patients with ESFT, investigational targeted or novel therapies along with future promises.

Ewing's Sarcoma and Peripheral Primitive Neuroectodermal Tumor of Bone and Soft Tissue

The histological diagnosis of Ewing's sarcoma (Es) continues to be a difficult task for pathologists. A number of new Es varieties has been described, leading to further complexity. Conventional Es, atypical Es, and peripheral neuroectodermal tumor (pPNET), including peripheral neuroepithelioma, belong genetically to the same family of neoplasms, displaying common chromosomal rearrangements and analogous gene reorganizations. The main translocations are t(11;22) and t(21;22), with genes EWS, FLI-1 and ERG being involved, as well as other members of the ETS family of transcription factors. The prevalence of morphology should be maintained with the use of conventional histological techniques and supported with the analysis of the expression of CD99 Mic2 (HBA 71, 0.13) antigen, which is present in over 90% of cases, as well as with FLI-1 rearranged gene derived protein. Moreover, FISH and RT-PCR in paraffin-embedded tumor tissue may be of use in extremely difficult cases for differential diagnosis. Nevertheless, a number of mixed tumor types, such as primitive sarcoma or biphenotypic sarcoma, may show structural and genetic diversity, thus rendering their diagnosis even more complex.

Synovial Sarcoma Microvesicles Harbor the SYT-SSX Fusion Gene Transcript: Comparison of Different Methods of Detection and Implications in Biomarker Research

Background. Synovial sarcoma is an aggressive soft-tissue malignancy. This study examines the presence of the SYT-SSX fusion transcript in synovial sarcoma microvesicles as well as its potential role as a biomarker for synovial sarcoma. Patients and Methods. Microvesicle release of synovial sarcoma cells was examined by transmission electron microscopy. RNA-content was analyzed by qPCR, nested PCR, nested qPCR, and droplet digital PCR to compare their sensitivity for detection of the SYT-SSX fusion gene transcript. Whole blood RNA, RNA of mononuclear cells, and microvesicle RNA of synovial sarcoma patients were analyzed for the presence of the fusion gene transcripts. Results. Electron microscopic analysis revealed synovial sarcoma cells releasing membrane-enclosed microvesicles. In vitro, the SYT-SSX fusion gene transcript was detected in both synovial sarcoma cells and microvesicles. Nested qPCR proved to be the most sensitive in detecting the SYT-SSX fusion gene mRNA. In contrast, the fusion gene transcript was not detected in peripheral blood cells and microvesicles of synovial sarcoma patients. Conclusion. Synovial sarcoma cells release microvesicles harboring the SYT-SSX fusion transcript. Nested qPCR proved to be the most sensitive in detecting the SYT-SSX fusion gene mRNA; however, more sensitive assays are needed to detect cancer-specific microvesicles in the peripheral blood of cancer patients.

Ewing Sarcoma: Current Management and Future Approaches Through Collaboration

Ewing sarcoma (ES) is an aggressive sarcoma of bone and soft tissue occurring at any age with a peak incidence in adolescents and young adults. The treatment of ES relies on a multidisciplinary approach, coupling risk-adapted intensive neoadjuvant and adjuvant chemotherapies with surgery and/or radiotherapy for control of the primary site and possible metastatic disease. The optimization of ES multimodality therapeutic strategies has resulted from the efforts of several national and international groups in Europe and North America and from cooperation between pediatric and medical oncologists. Successive first-line trials addressed the efficacy of various cyclic combinations of drugs incorporating doxorubicin, vincristine, cyclophosphamide, ifosfamide, etoposide, and dactinomycin and identified prognostic factors now used to tailor therapies. The role of high-dose chemotherapy is still debated. Current 5-year overall survival for patients with localized disease is 65% to 75%. Patients with metastases have a 5-year overall survival < 30%, except for those with isolated pulmonary metastasis (approximately 50%). Patients with recurrence have a dismal prognosis. The many insights into the biology of the EWS-FLI1 protein in the initiation and progression of ES remain to be translated into novel therapeutic strategies. Current options and future approaches will be discussed.

Optimization of rhabdomyosarcoma disseminated disease assessment by flow cytometry

Rhabdomyosarcoma (RMS) is the most common type of soft tissue sarcoma in children. Circulating tumor cells in peripheral blood or disseminated to bone marrow, a concept commonly referred to as minimal residual disease (MRD), are thought to be key to the prediction of metastasis and treatment efficacy. To date, two MRD markers, MYOD and MYOGENIN, have been tested; however, MRD detection continues to be challenging mainly owing to the closeness of the detection limit and the discordance of both markers in some samples. Therefore, the addition of a third marker could be useful for more accurate MRD assessment. The PAX3 gene is expressed during embryo development in all myogenic precursor cells in the dermomyotome. As RMS cells are thought to originate from these muscle precursor cells, they are expected to be positive for PAX3. In this study, PAX3 expression was characterized in cancer cell lines and tumors, showing wide expression in RMS. Detection sensitivities by quantitative polymerase chain reaction (qPCR) of the previously proposed markers, MYOD and MYOGENIN, were similar to that of PAX3, thereby indicating the feasibility of its detection. Interestingly, the flow cytometry experiments supported the usefulness of this technique in the quantification of MRD in RMS using PAX3 as a marker. These results indicate that flow cytometry, albeit in some cases slightly less sensitive, can be considered a good approach for MRD assessment in RMS and more consistent than qPCR, especially owing to its greater specificity. Furthermore, fluorescence-activated cell sorting permits the recovery of cells, thereby providing material for further characterization of circulating or disseminated cancer cells.

Detection of common chromosomal translocations in small round blue cell pediatric tumors

BACKGROUND AND AIMS

Recurrent and specific chromosomal translocations have been described in four pediatric sarcomas belonging to the small round blue cell (SRBC) group of tumors. Identification of mRNA chimeras using RT-PCR discriminates among alveolar rhabdomyosarcoma (ARMS), Ewing's sarcoma (ES/pPNET), synovial sarcoma (SS) and desmoplastic small round cell tumor (DSRCT); however, frequencies of these translocations are variable. We present a retrospective study comparing histological examination and occurrence of major chromosomal translocations to validate the diagnosis and to assess the frequency of these molecular markers in a group of 92 small round blue cell (SRBC) tumor samples from Hospital Infantil de Mexico.

METHODS

We tested a panel of RT-PCR assays to each RNA tumor sample from formalin-fixed, paraffin-embedded tumors to detect specific mRNA chimeras in 47 ES/pPNET, 19 ARMS, four SS, three DSRCT, and 19 other SRBC tumors.

RESULTS

After excluding poor RNA quality samples, we found translocations in 17/31 ES/pPNET (54.8%), 10/19 ARMS (52.6%), 4/4 SS (100%) and 4/4 DSRCT (100%). We found disagreement in only three samples: one ES/pPNET and one embryonal rhabdomyosarcoma harbor a PAX3-FOXO1 translocation (for ARMS), and one neuroepithelioma harboring a EWS-WT1 (for DSRCT). Unsuitable RNA was found in 20/92 samples (21.7%) and was related to necrosis, small amount of tumor tissue, and use of nitric acid in bone biopsies, but was not related to age of the block.

CONCLUSIONS

We found a significantly lower occurrence of chromosomal translocations in ES/pPNET compared to reports from other groups. Differences may exist in the frequencies of these molecular markers among different populations.

The EWS/FLI Oncogene Drives Changes in Cellular Morphology, Adhesion, and Migration in Ewing Sarcoma

Ewing sarcoma is a tumor of the bone and soft tissue caused by the expression of a translocation-derived oncogenic transcription factor, EWS/FLI. Overt metastases are associated with a poor prognosis in Ewing sarcoma, but patients without overt metastases frequently harbor micrometastatic disease at presentation. This suggests that the metastatic potential of Ewing sarcoma exists at an early stage during tumor development. We have therefore explored whether the inciting oncogenic event in Ewing sarcoma, EWS/FLI, directly modulates tumor cell features that support metastasis, such as cell adhesion, cell migration, and cytoarchitecture. We used an RNAi-based approach in patient-derived Ewing sarcoma cell lines. Although we hypothesized that EWS/FLI might induce classic metastatic features, such as increased cell adhesion, migration, and invasion (similar to the phenotypes observed when epithelial malignancies undergo an epithelial-to-mesenchymal transition during the process of metastasis), surprisingly, we found the opposite. Thus, EWS/FLI expression inhibited the adhesion of isolated cells in culture and prevented adhesion in an in vivo mouse lung assay. Cell migration was similarly inhibited by EWS/FLI expression. Furthermore, EWS/FLI expression caused a striking loss of organized actin stress fibers and focal adhesions and a concomitant loss of cell spreading, suggesting that EWS/FLI disrupts the mesenchymal phenotype of a putative tumor cell-of-origin. These data suggest a new paradigm for the dissemination and metastasis of mesenchymally derived tumors: these tumors may disseminate via a "passive/stochastic" model rather than via an "active" epithelial-to-mesenchymal type transition. In the case of Ewing sarcoma, it appears that the loss of cell adhesion needed to promote tumor cell dissemination might be induced by the EWS/FLI oncogene itself rather than via an accumulation of stepwise mutations.

Assessment of minimal residual disease in ewing sarcoma

Advances in molecular pathology now allow for identification of rare tumor cells in cancer patients. Identification of this minimal residual disease is particularly relevant for Ewing sarcoma, given the potential for recurrence even after complete remission is achieved. Using RT-PCR to detect specific tumor-associated fusion transcripts, otherwise occult tumor cells are found in blood or bone marrow in 20–30% of Ewing sarcoma patients, and their presence is associated with inferior outcomes. Although RT-PCR has excellent sensitivity and specificity for identifying tumor cells, technical challenges may limit its widespread applicability. The use of flow cytometry to identify tumor-specific antigens is a recently described method that may circumvent these difficulties. In this manuscript, we compare the advantages and drawbacks of these approaches, present data on a third method using fluorescent in situ hybridization, and discuss issues affecting the further development of these strategies.

Comprehensive analysis of published phase I/II clinical trials between 1990-2010 in osteosarcoma and Ewing sarcoma confirms limited outcomes and need for translational investment

Background

High grade primary bone sarcomas are rare cancers that affect mostly children and young adults. Osteosarcoma and Ewing sarcoma are the most common histological subtypes in this age group, with current multimodality treatment strategies achieving 55-70% overall survival. As there remains an urgent need to develop new therapeutic interventions, we have reviewed published phase I/II trials that have been reported for osteosarcoma and Ewing sarcoma in the last twenty years.

Results

We conducted a literature search for clinical trials between 1990 and 2010, either for trials enrolling bone sarcoma patients as part of a general sarcoma indication or trials specifically in osteosarcoma and Ewing sarcoma. We identified 42 clinical trials that fulfilled our search criteria for general sarcoma that enrolled these patient groups, and eight and twenty specific trials for Ewing and osteosarcoma patients, respectively. For the phase I trials which enrolled different tumour types our results were incomplete, because the sarcoma patients were not mentioned in the PubMed abstract. A total of 3,736 sarcoma patients were included in these trials over this period, 1,114 for osteosarcoma and 1,263 for Ewing sarcoma. As a proportion of the worldwide disease burden over this period, these numbers reflect a very small percentage of the potential patient recruitment, approximately 0.6% for Ewing sarcoma and 0.2% for osteosarcoma. However, these data show an increase in recent activity overall and suggest there is still much room for improvement in the current trial development structures.

Conclusion

Lack of resources and commercial investment will inevitably limit opportunity to develop sufficiently rapid improvements in clinical outcomes. International collaboration exists in many well founded co-operative groups for phase III trials, but progress may be more effective if there were also more investment of molecular and translational research into disease focused phase I/II clinical trials. Examples of new models for early translational and early phase trial collaboration include the European based EuroBoNeT network, the Sarcoma Alliance for Research through Collaboration network (SARC) and the new European collaborative translational trial network, EuroSarc.

Diagnosis and prognosis for the Ewing family of tumors

BACKGROUND

Ewing's sarcoma was first described by James Ewing in 1921. It is the second most common bone sarcoma seen in children, adolescents and young adults after osteosarcoma and belongs to the group of 'small round blue cell tumors', showing an aggressive natural history. Once almost invariably fatal and treated only with palliative radiation, thanks to a multidisciplinary approach, the probability of survival at 5 years is now ∼ 65 - 75% for patients with localized disease. This percentage is no more than 20 - 25% for patients with metastatic disease at presentation.

OBJECTIVE

To review epidemiology, diagnosis and prognosis of Ewing's sarcoma family tumors (EFT) of bone. This entity includes a wide spectrum of tumors, from the less differentiated or classic Ewing's sarcoma to the more differentiated peripheral neuroectodermal tumor. A translocation involving the EWS gene on the chromosome 22 band q12 is characteristic of EFTs.

CONCLUSION

A complete clinical and radiological assessment is essential for initial patient evaluation. Owing to the rarity of this entity, whenever an EFT is suspected patients should be referred to a bone tumor treatment center before a diagnostic biopsy is performed. The molecular characterization of chromosomal translocations has an important role in the diagnosis of EFT.

Consensus criteria for sensitive detection of minimal neuroblastoma cells in bone marrow, blood and stem cell preparations by immunocytology and QRT-PCR: recommendations by the International Neuroblastoma Risk Group Task Force

Disseminating disease is a predictive and prognostic indicator of poor outcome in children with neuroblastoma. Its accurate and sensitive assessment can facilitate optimal treatment decisions. The International Neuroblastoma Risk Group (INRG) Task Force has defined standardised methods for the determination of minimal disease (MD) by immunocytology (IC) and quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) using disialoganglioside G(D2) and tyrosine hydroxylase mRNA respectively. The INRG standard operating procedures (SOPs) define methods for collecting, processing and evaluating bone marrow (BM), peripheral blood (PB) and peripheral blood stem cell harvest by IC and QRT-PCR. Sampling PB and BM is recommended at diagnosis, before and after myeloablative therapy and at the end of treatment. Peripheral blood stem cell products should be analysed at the time of harvest. Performing MD detection according to INRG SOPs will enable laboratories throughout the world to compare their results and thus facilitate quality-controlled multi-centre prospective trials to assess the clinical significance of MD and minimal residual disease in heterogeneous patient groups.

Emerging chemotherapeutic strategies and the role of treatment stratification in Ewing sarcoma

The Ewing sarcoma family of tumors (ESFT) is one of the most common groups of malignancies arising in children, adolescents, and young adults up to approximately 25 years of age. It comprises Ewing sarcoma arising from bone and extraosseous Ewing sarcoma arising from soft tissues (which includes peripheral neuroectodermal tumors and Askin tumor arising from the chest wall). Ewing sarcoma is treated successfully in many cases by a combination of chemotherapy, surgery, and radiotherapy. A number of prognostic factors have been identified that can be used to stratify patients according to the risk of relapse, allowing optimization of treatment. These can be categorized as tumor-related factors (presence of metastases, tumor site, volume, lactic dehydrogenase level, chromosomal translocation type, presence of fusion transcripts in blood and bone marrow), treatment-related factors (local therapy, histologic response to chemotherapy, radiologic response to chemotherapy, chemotherapy regimen), and patient-related factors (gender, age). Newer chemotherapeutic agents are currently being investigated, and there is now increasing interest in the identification of molecular targets in ESFT that could be exploited therapeutically, which include the mammalian target of rapamycin (mTOR) and insulin growth factor-1 (IGF-1) receptor pathways.

Gene expression profile of ewing sarcoma cell lines differing in their EWS-FLI1 fusion type

The t(11;22)(q24;q12) translocation is present in up to 95% of Ewing tumor patients and results in the formation of an EWS-FLI-1 fusion gene that encodes a chimeric transcription factor. Many alternative forms of EWS-FLI-1 exist because of variations in the location of the EWS and FLI-1 genomic breakpoints. Previous reports have shown that the type 1 fusion is associated with a significantly better prognosis than the other fusion types. It has been suggested that the observed clinical discrepancies result from different transactivation potentials of the various EWS-FLI-1 fusion proteins. In an attempt to identify genes whose expression levels are differentially modulated by structurally different EWS-FLI-1 transcription factors, we have used microarray technology to interrogate 19,000 sequence genes to compare gene expression profile of type 1 or non-type 1 Ewing sarcoma cell lines. Data analysis showed few qualitative differences on gene expression; expression of only 41 genes (0.215% of possible sequences analyzed) differed significantly between Ewing tumor cell lines carrying EWS-FLI-1 fusion type 1 with respect to those with non-type 1 fusion.

Molecular diagnosis of Ewing's sarcoma/primitive neuroectodermal tumor in formalin-fixed paraffin-embedded tissues by RT-PCR and fluorescence in situ hybridization

Recent studies have suggested that formalin-fixed paraffin-embedded (FFPE) tissues can be used for molecular analyses by fluorescence in situ hybridization (FISH) and RT-PCR. We analyzed 18 cases of ES/PNET for the t(11;22)(q24;q12) and t(21;22)(q22;q12) fusion transcripts by RT-PCR and analyzed for EWS translocation by interphase FISH with a dual color fusion probe to compare these two approaches directly. RT-PCR detected 13 (72%) EWS-FLI-1 fusions (type I=10, type II=3) and 2 (11%) EWS-ERG fusions. Three cases could not be evaluated because the housekeeping gene phosphoglycerate kinase (internal mRNA control) was not amplified. FISH was diagnostic in 15 of 18 cases (83%). There were three discordant cases between RT-PCR and FISH (concordance of 83%). Using a combination of RT-PCR and FISH, the results were complementary. One advantage of RT-PCR analysis was that subtypes of EWS translocation could be determined specifically (type I, type II and ERG). These findings indicate that because of the difficulties and limitations associated with the molecular analysis of FFPE tissues, a combination of RT-PCR and FISH may be a better approach to enhance the sensitivity and accuracy of detecting ES/PNET translocations in FFPE tissues with suboptimally preserved nucleic acids.

Tumor cells are present in stem cell harvests of Ewings sarcoma patients and their persistence following transplantation is associated with relapse

BACKGROUND

Tumor cells frequently contaminate autologous stem cell products in a variety of malignancies, but their clinical significance remains controversial. We retrospectively monitored tumor contamination in stem cell harvests from patients with Ewing family of tumors (EFT) all harboring the specific translocation EWS-FLI-1 that characterize these tumors.

PROCEDURE

Twenty- seven harvests from 11 patients were included in the study. In addition, 6 and 19 bone marrow (BM) or peripheral blood (PBL) samples were available before and after transplantation, respectively, for RT-PCR and nested PCR analyzes.

RESULTS

All 11 patients had contaminating tumor cells in their harvests. All samples prior to transplantation were RT-PCR positive. Two out of the 11 patients who underwent transplantation died of complications. Out of the remaining nine patients, two are alive and well 68 and 84 months from diagnosis, and are the only patients with no detectable tumor cells in their samples after transplantation. One of these patients harbored contaminating tumor cells in only one of the two harvests collected. Seven patients relapsed after transplant, and in four patients BM/PBL samples were available prior to the clinical relapse. All these samples harbored contaminating tumor cells.

CONCLUSIONS

We suggest a possible correlation between the amount of contaminating cells in the harvest and relapse after transplantation. Quantitative RT-PCR studies of the chimeric transcripts are underway to explore this issue.

The predictive potential of molecular detection in the nonmetastatic Ewing family of tumors

BACKGROUND

Tumors in the Ewing family (EFTs) are the second most common bone tumors in children and adolescents. Despite aggressive chemotherapy, one-third of patients with localized tumor still may develop recurrences. This implies that not all tumor cells are eradicated and that the patients may have a level of residual disease. EFTs are characterized by specific chromosomal translocations that result in chimeric transcripts that can be detected with reverse transcriptase-polymerase chain reaction (RT-PCR) analysis.

METHODS

The authors report the prognostic potential of the positive chimeric transcript (EWS/FLI1) in bone marrow (BM) and/or peripheral blood (PBL) in 26 patients with EFT during a long follow-up period (median, 61 months).

RESULTS

At diagnosis, 43% of patients had positive RT-PCR BM results, with no correlation to tumor progression (P = 0.3). During follow-up, 58% of patients had positive RT-PCR results in their last sample analyzed (BM and/or PBL). A highly significant correlation between the presence of the chimeric transcript and disease progression was detected (P = 0.0028). In a multivariate analysis, the percentage of tumor necrosis (P = 0.007) and RT-PCR results during follow-up (P = 0.02) remained significant prognostic markers. In 10 of 11 patients who developed disease progression, BM and/or PBL samples were positive for the chimeric transcript before evidence of overt clinical recurrence.

CONCLUSIONS

Occult tumor cells in BM and/or PBL samples during long follow-up are strong predictors of recurrent disease in patients with nonmetastatic EFTs.

Association Between Telomerase Activity and Outcome in Patients With Nonmetastatic Ewing Family of Tumors

Purpose: Telomerase is considered a molecular marker for malignancy. The aim of this study was to determine telomerase activity (TA) as a prognostic factor at diagnosis and as a marker for minimal residual disease during therapy and follow-up in nonmetastatic Ewing family of tumors (EFT).

Patients and Methods: Primary tumor specimens and 97 peripheral blood (PBL) samples from 31 EFT patients were analyzed for TA by the Telomeric Repeat Amplification Protocol (TRAP assay). The telomerase catalytic subunit (human telomerase reverse transcriptase [hTERT]) gene expression was evaluated by quantitative reverse transcriptase polymerase chain reaction (RT-PCR) and telomere length was determined by Southern blotting. The presence of the EFT chimeric transcripts was analyzed by RT-PCR. Correlations with progression-free survival were evaluated.

Results: At diagnosis, TA in primary tumors did not correlate with outcome. During therapy and follow-up, highly significant correlation was observed between high TA in PBL samples and adverse prognosis (P < .0001). None of the patients harboring low TA progressed, with a long follow-up (median, 60 months) and a progression-free survival (PFS) of 100%. In nine patients, high TA actually could predict relapse, long before overt clinical relapse. The group of patients with high TA and positive RT-PCR had the most adverse outcome; PFS of 20% (P = .0025). TA was found to be a better prognostic factor than RT-PCR and histopathologic response at surgery.

Conclusion: The results suggest that TA is a significant prognostic variable, superior to the established clinical prognostic parameters during therapy and tumor surveillance. It could be used in combination with RT-PCR for a new risk classification.

Ewing's sarcoma: diagnostic, prognostic, and therapeutic implications of molecular abnormalities

The identification of the non-random chromosome rearrangements between the EWS gene on chromosome 22q12 and members of the ETS gene family in Ewing's sarcoma, peripheral primitive neuroectodermal tumour, Askin tumour, and neuroepithelioma has been a key advance in understanding their common histogenesis and defining the Ewing's sarcoma family of tumours (ESFT). In addition to improvements in diagnosis and potentially the stratification of patients for risk, biological investigations of these gene fusions may define targets for much needed therapeutic strategies to eliminate minimal residual disease or metastatic disease. Insight into their relation with other oncogenic events in ESFT will advance risk group analysis and ultimately may improve clinical management and survival for patients with this disease.

A systematic review of molecular and biological markers in tumours of the Ewing's sarcoma family

The aims of this study were to perform the first systematic review of molecular and biological tumour markers in tumours of the Ewing's sarcoma family (ESFT), and evaluate the current evidence for their clinical use. A well-defined, reproducible search strategy was used to identify the relevant literature from 1966 to February 2000. Papers were independently assessed for tumour markers used in the screening, diagnosis, prognosis or monitoring of patients with ESFT. Eighty-four papers studying the use of 70 different tumour markers in ESFT's were identified. Low-quality, inconsistent reporting limited meta-analysis to that of prognostic data for 28 markers. Patients with tumours lacking S-100 protein expression have a better overall survival (OS) (hazard ratio (HR)=0.41, 95% confidence interval (CI) 0.19, 0.89) than those with expression; patients with high levels of serum LDH had a worse OS and disease-free survival (DFS) (OS: HR=2.92, CI 2.16, 3.94, DFS: HR=3.38, 95% CI 2.28, 4.99); patients with localised disease and tumours expressing type 1 EWS-FLI1 fusion transcripts had an improved DFS compared with those with other fusion transcript types (HR=0.17, 95% CI 0.079, 0.37). The knowledge base formed should facilitate more informative future research. Improved statistical reporting and large, multicentre prospective studies are advocated.

Increased risk of systemic relapses associated with bone marrow micrometastasis and circulating tumor cells in localized ewing tumor

PURPOSE

The presence of metastasis is a major prognostic factor in Ewing tumor (ET). The relapse pattern of patients with localized tumors has long indicated that cases with disseminated ET cells escape detection at diagnosis. ET cells are characterized by specific gene fusions that can be detected with high sensitivity and specificity by reverse transcriptase polymerase chain reaction (RT-PCR).

PATIENTS AND METHODS

RT-PCR targeting EWS-FLI-1 or EWS-ERG transcripts was used to search for occult tumor cells in peripheral blood (PB) and bone marrow (BM) at diagnosis in 172 patients with ET, and the prognostic significance of this parameter was assessed.

RESULTS

As we suggested previously in a smaller series of patients, RT-PCR positivity of the BM was correlated with a high risk of adverse outcome in the overall study population (P =.007). More interestingly, among patients with otherwise localized tumors, BM micrometastasis also predicted significantly poorer disease-free survival rates (P =.043). The presence of circulating tumor cells (CTC) was more frequently observed in patients with large tumors (P =.006). CTC were associated with a poor outcome among patients with clinically localized disease (P =.045). Patients with clinically localized disease and peripheral occult tumor cells as evidenced by BM and/or PB RT-PCR positivity had axial or proximal tumors and experienced relapses at a systemic rather than at a local level.

CONCLUSION

Patients with localized ET and BM micrometastasis or CTC are comparable to patients with metastases in terms of the localization of the primary tumor, outcome, and relapse pattern.

Risk assignment in pediatric soft-tissue sarcomas: an evolving molecular classification

Pediatric soft-tissue sarcomas are increasingly being defined by both histologic appearance and underlying chromosomal abnormalities to determine their biologic behavior. Most sarcomas of this type have specific chromosomal translocations that create unique fusion genes. Expression of such fusion genes may have diagnostic, prognostic, and surveillance implications for the patient. This review analyzes the fusion gene expressions seen with seven of the major types of pediatric soft-tissue tumors and their impact on biologic behavior. In nearly 50% of the malignancies discussed, the diagnostic, prognostic, and surveillance implications of their specific fusion gene expressions are already defined or becoming established (alveolar rhabdomyosarcoma, Ewing sarcoma/primitive neuroectodermal tumor, and synovial sarcoma). In the remainder of the tumors, these questions are rapidly being addressed. To facilitate future fusion gene studies, pediatric surgeons, pathologists, and oncologists need to work as a coordinated team to ensure proper tumor procurement. Large clinical cooperative trials involving biologic studies of pediatric soft-tissue sarcomas could facilitate advancement of knowledge in this area of pediatric oncology.

Differentiating lymphoblastic lymphoma and Ewing's sarcoma: lymphocyte markers and gene rearrangement

We encountered a child with an intraosseous small round cell tumor that was negative for LCA, CD20 (L26), and CD3 and positive for vimentin, CD99 (MIC-2), and periodic acid-Schiff. The tumor exhibited rosette-like formations. This case was initially interpreted as Ewing's sarcoma (ES); however, additional studies revealed positivity for CD79a, CD43, and TdT expression, and an immunoglobulin heavy chain gene rearrangement (IgH-R) by polymerase chain reaction (PCR) established this to be a precursor B-lymphoblastic lymphoma. Because the differential diagnosis of ES and lymphoblastic lymphoma can be difficult and the differential diagnostic value of leukocyte antigens and immunoglobulin heavy chain gene rearrangement studies have not been fully evaluated, we conducted a more extensive investigation on 33 (21 soft tissue and 12 intraosseous) ES cases. Cases were retrieved from the files of the Department of Pathology at Georgetown University and from the Soft Tissue Registry of the Armed Forces Institute of Pathology. The cases were studied by light microscopy, immunohistochemistry, and PCR for IgH-R and T cell receptor gamma chain gene rearrangement (Tgamma-R). There were 17 females and 16 males; the mean age was 29.3 years. Locations included the extremities (n = 17) and trunk (n = 16). All cases fit the ES spectrum by light microscopy and immunohistochemistry, as previously determined, and were negative for lymphoid markers (LCA, CD3, CD20, CD43, CD79a, and TdT), CD10 and CD34. CD99 was positive in 31/33 and bcl-2 was weakly positive in 13/33 cases. All 21 cases studied for gene rearrangements by PCR were negative for IgH-R and Tgamma-R. Distinction of intraosseous lymphoblastic lymphoma from ES may be difficult because lymphomas may occasionally exhibit unexpected morphologic and immunophenotypic properties including LCA, CD3 and CD20 negativity and cytokeratin positivity. Additional analysis using CD79a, CD43, TdT, and PCR should be performed to avoid misdiagnosis. True ES is negative for lymphoid markers including CD79a, CD43, and TdT, as well as for IgH-R and Tgamma-R.

No EWS/FLI1 fusion transcripts in giant-cell tumors of bone

Giant-cell tumor of bone (GCT) is a locally aggressive neoplasm of unknown etiology and pathogenesis. Cytogenetically, no consistent chromosomal alterations, apart from telomeric associations involving various chromosome ends, have been described. Recently, however, it was reported that by using highly sensitive nested RT-PCR, a high proportion of GCT displays chimeric EWS/FLI1 fusion transcripts, i.e., the molecular genetic feature previously known to be strongly associated with the Ewing family of tumors. Thus, we decided to perform single-step and nested RT-PCR analyses on fresh frozen samples from 10 cases of GCT, all of which had also been subjected to cytogenetic analysis. After short-term culturing, none of the samples displayed any t(11;22)(q24;q12), the translocation characteristically giving rise to the EWS/FLI1 fusion, nor any other type of rearrangement of 11q24 or 22q12. Furthermore, in none of the cases did the RT-PCR analysis, whether single step or nested, result in products corresponding to a hybrid EWS/FLI1 transcript. On the basis of these results, we conclude that translocations leading to fusion of the EWS and FLI1 genes are not part of the pathogenesis of GCT.

Immunomagnetic purging of Ewing's sarcoma from blood and bone marrow: quantitation by real-time polymerase chain reaction

PURPOSE

A propensity for hematogenous spread with resulting contamination of autologous cell products complicates cellular therapies for Ewing's sarcoma. We used a new approach to purge artificially contaminated cellular specimens of Ewing's sarcoma and show the capacity for real-time polymerase chain reaction (PCR) to quantify the contamination level of Ewing's sarcoma in such specimens.

PATIENTS AND METHODS

Binding of monoclonal antibody (MoAb) 8H9 to Ewing's sarcoma cell lines and normal hematopoietic cells was studied using flow cytometry. Using real-time PCR--based amplification of t(11;22), levels of Ewing's contamination of experimental and clinical cellular products were monitored. Purging was accomplished using immunomagnetic-based depletion. Monitoring of the function of residual hematopoietic progenitors and T cells was performed using functional assays.

RESULTS

MoAb 8H9 shows binding to Ewing's sarcoma but spares normal hematopoietic tissues. Nested real-time PCR is capable of detecting contaminating Ewing's sarcoma cells with a sensitivity of one cell in 10(6) normal cells. After 8H9-based purging, a 2- to 3-log reduction in contaminating Ewing's sarcoma was shown by real-time PCR, with purging to PCR negativity at levels of contamination of 1:10(6). Levels of contamination in clinical samples ranged from 1:10(5) to 10(6). Therefore, 8H9-based purging of clinical samples is predicted to reduce tumor cell contamination to a level below the limit of detection of PCR.

CONCLUSION

These results demonstrate a new approach for purging contaminated cellular products of Ewing's sarcoma and demonstrate the capacity of real-time PCR to provide accurate quantitative estimates of circulating tumor burden in this disease.

Molecular analysis of the 9p21 locus and p53 genes in Ewing family tumors

SUMMARY

The EWS-ETS rearrangements, and their respective fusion gene products, are specifically associated with histopathologically Ewing family tumors (EFT). These translocations are implicated in generating malignant transformation of EFT, but the presence of additional genetic alterations must be considered in the pathogenesis of such tumors. We analyzed 26 samples (biopsies and/or nude mice xenotransplants) collected from 19 patients with an EFT to determine whether molecular and cytogenetic alterations of the G(1)/S checkpoint genes are implicated in the pathogenesis of EFT. We found inactivating p53 mutations in three (16%) cases, which correlated with a loss of p21(WAF1/Cip1) expression and with a monosomy of chromosome 17 in two cases. Homozygous deletion of the p16(INK4A)/p14(ARF) gene was detected in four (21%) cases, three with codeletion of the p15(INK4B) gene and with chromosome 9 abnormalities. In all of these cases, expression of the implicated genes was absent. Hypermethylation of the p16(INK4A) and p15(INK4B) genes was detected in two (10%) and three (16%) cases, respectively, and was correlated with a low level of gene expression. Neither cyclin D1, nor MDM2 and CDK4 amplification was observed. Kaplan-Meier analysis showed that patients with tumors carrying homozygous deletion of the 9p21 locus, or point mutations of the p53 gene, had poorer outcomes than those without these molecular alterations (p = 0.005). In conclusion, 58% (11 of 19) of the analyzed patients showed genetic or epigenetic alterations in either the 9p21 locus or p53 tumor suppressor genes, defining a subgroup of patients with poor clinical outcome. This fact points to an important role of the G(1)/S cell cycle checkpoint dysregulation in the pathogenesis of EFT.

High-dose melphalan, etoposide, total-body irradiation, and autologous stem-cell reconstitution as consolidation therapy for high-risk Ewing's sarcoma does not improve prognosis

PURPOSE

To determine whether consolidation therapy with high-dose melphalan, etoposide, and total-body irradiation (TBI) with autologous stem-cell support would improve the prognosis for patients with newly diagnosed metastatic Ewing's sarcoma (ES).

PATIENTS AND METHODS

Thirty-two eligible patients with newly diagnosed ES metastatic to bone and/or bone marrow were enrolled onto this study. Treatment was initially comprised of five cycles of induction chemotherapy (cyclophosphamide, doxorubicin, and vincristine alternating with ifosfamide and etoposide) and local control. Peripheral-blood stem-cell collection was performed after the second cycle of chemotherapy, with delay if the bone marrow was persistently involved. If patients had a good response to initial therapy, they proceeded to consolidation therapy with melphalan, etoposide, TBI, and stem-cell support.

RESULTS

Of the 32 eligible patients, 23 proceeded to high-dose therapy consolidation. Of the nine patients who did not proceed to consolidation, four were secondary to progressive disease and two were secondary to toxicity. Three patients died from toxicity during the high-dose phase of the therapy. The majority of the patients who underwent high-dose consolidation therapy experienced relapse and died with progressive disease. Two-year event-free survival (EFS) for all eligible patients is 20%. The 2-year post-stem-cell reconstitution EFS for the subset of 23 patients who received consolidation therapy is 24%. Analysis of peripheral-blood stem-cell collections by molecular techniques for minimal residual disease showed contamination of at least some samples by tumor cells in all three patients with available data.

CONCLUSION

Consolidation with high-dose melphalan, etoposide, TBI, and autologous stem-cell support failed to improve the probability of EFS in this cohort of patients with newly diagnosed metastatic ES.

Molecular characterization of minimal residual cancer cells in patients with solid tumors

The failure to reduce the mortality of patients with solid tumors is mainly a result of the early dissemination of cancer cells to secondary sites, which is usually missed by conventional diagnostic procedures used for tumor staging. PCR was shown to be superior to conventional techniques in detecting circulating tumor cells and micrometastases allowing the identification of one tumor cell in up to 10(7) normal cells in various sources such as blood, bone marrow, lymph nodes, urine or stool. The methods used are based on the detection of either genomic alterations in oncogenes and tumor suppressor genes or on the mRNA expression of tissue-specific and tumor-associated genes. The additional implementation of techniques for cancer cell purification had a significant impact on analytical sensitivity and specificity of MRCC detection. For patients with e.g. melanoma, breast, colorectal or prostate cancer it was demonstrated that the presence of disseminated cancer cells defines a subgroup of patients with reduced time to recurrence. The possibility to use easily accessible body fluids as a source for MRCC detection enables longitudinal observations of the disease. In this review we discuss the potential of molecular characterization of MRCC as a tool to improve prognostication, therapy selection and drug targeting as well as therapy monitoring.

PCR techniques for clonality assays

Clonal overgrowths represent the hallmark of neoplastic proliferations, and their demonstration has been proved useful clinically for the diagnosis of malignant lymphomas based on the detection of specific and dominant immunoglobulin and/or T-cell receptor gene rearrangements. Nonrandom genetic alterations can also be used to test clonal expansions and the clonal evolution of neoplasms, especially analyzing hypervariable deoxyribonucleic acid (DNA) regions from patients heterozygous for a given marker. These tests rely basically on the demonstration of loss of heterozygosity (LOH) resulting from either hemizygosity (nonrandom interstitial DNA deletions) or homozygosity of mutant alleles observed in neoplasms. LOH analyses identify clonal expansions of a tumor cell population, and point to monoclonal proliferation when multiple and consistent LOH are demonstrated. Based on the methylation-related inactivation of one X chromosome in female subjects, X-linked markers (e.g., androgen receptor gene) will provide clonality information using LOH analyses after DNA digestion with methylation-sensitive restriction endonucleases. Therefore, both non-X-linked and X-linked analyses give complementary information, related and not related to the malignant transformation pathway respectively. Applied appropriately, these tools can establish the clonal evolution of tumor cell populations (tumor heterogeneity), identify early relapses, distinguish recurrent tumors from other metachronic neoplasms, and differentiate field transformation from metastatic tumor growths in synchronic and histologically identical neoplasms.

Ewing tumor: tumor biology and clinical applications

The Ewing tumor family includes classical Ewing's sarcoma of bone and soft tissues, peripheral primitive neuroectodermal tumors (pPNET), Askin tumor, and other less frequent variants. This group of tumors is defined by the consistent presence of chromosomal translocations resulting in gene fusions between EWS gene and a member of the ETS family of transcription factors, mainly FLI1 and ERG. Analogous fusions are seen in other solid developmental tumors, like desmoplastic small round cell tumor. These fusions, which are consistently present and tumor-specific, control transcription of several target genes, largely unknown but critical to cell proliferation and differentiation. Therefore, gene fusions are useful to diagnose and classify small round cell tumors, have prognostic significance, are probably useful to detect micrometastasis and monitor minimal residual disease, and are potential therapeutic targets. Secondary molecular alterations, which include mutations of cell cycle regulatory genes, are not tumor-specific but are related to progression and may have prognostic value. The Ewing tumor family represents a paradigm of the application of the knowledge of biology of neoplasia to the clinical management of patients.

Soft tissue Ewing sarcoma--peripheral primitive neuroectodermal tumor with atypical clear cell pattern shows a new type of EWS-FEV fusion transcript

This study describes a new case of Ewing sarcoma (ES)-peripheral primitive neuroectodermal tumor (pPNET) with unusual phenotype and fusion gene structure. The tumor located in the inguinal area of a 15-year-old boy showed a highly aggressive behavior with hematogenous metastases after intensive chemotherapy and bone marrow transplant, causing death 28 months after diagnosis. The tumor displayed a clear cell pattern, and several neuroectodermal markers proved positive both in the original tumor and in xenografts. This neuroectodermal character was confirmed by electron microscopy. Moreover, cytogenetically the tumor has an unusual chromosomal rearrangement, t(2;22)(q13;q22,t(3;18)(p21;q23); representing a new EWS-FEV fusion type in which exon 7 of EWS gene is fused with exon 2 of FEV gene. This is the third published study of an ES-pPNET showing EWS-FEV fusion described, but it is the first study of a tumor with the aforementioned fusion points. These findings support the genetic and morphologic heterogeneity existing within the group of ES-pPNET tumors.

A Practical Approach to the Differential Diagnosis of Small Round Cell Tumors of Infancy Using Recent Scientific and Technical Advances

Scientific and technical advances have direct impact on the day to day practice of surgical pathology. Pathologists must learn to use new findings to improve diagnostic classification and add clinically useful information in a fiscally responsible manner. The undifferentiated tumors of young people (historically referred to as small round cell tumors of infancy) are a useful example of how new information has become an important part of routine practice. This article describes a practical approach to the differential diagnosis of small round cell tumors using immunophenotypic and genetic analysis as an aid to increase confidence and diagnostic accuracy. Int J Surg Pathol 8(2):87-97, 2000

Molecular biology of the Ewing's sarcoma/primitive neuroectodermal tumor family

Ewing's sarcoma (ES) and primitive neuroectodermal tumor (PNET) are members of a tumor family consistently associated with chromosomal translocation and functional fusion of the EWS gene to any of several structurally related transcription factor genes. Similar gene fusion events occur in other mesenchymal and hematopoietic tumors and are tumor-specific. The resulting novel transcription factor-like chimeric proteins are believed to contribute to tumor biology by aberrant regulation of gene expression altering critical controls of cell proliferation and differentiation. These tumor-specific molecular rearrangements are useful for primary diagnosis, may provide prognostic information, and present potential therapeutic targets. The recent advances in our understanding of the molecular biology of ES and PNET represent a paradigm for the application of the basic biology of neoplasia to clinical management of patients.

The Ewing family of tumors and the search for the Achilles' heel

The ideal cancer therapy would accomodate the specific biology of a tumor and be based upon understanding the mechanisms of malignancy. This vision has been the driving force in cancer research. However, the story of success in clinical cancer management is a story of empirie largely independent from progress in basic research. For the Ewing family of tumors (EFT) comprising Ewing's sarcoma and peripheral primitive neuroectodermal tumor, significant insights into the molecular basis have appeared recently. Some of last year's discoveries may have taken us closer to the identification of the Achilles' heel in this disease. The first clue has been obtained to the mechanism of chromosomal translocation, which constitutes a rate-limiting step in EFT pathogenesis. Also, researchers have progressed in understanding the control of EFT cell proliferation, differentiation, and death. A major role in these processes has been attributed to the EWS-ets gene rearrangement. Specific growth factor circuits appear to be involved in deregulated tumor cell growth. By analogy to heterologous cellular systems, it is possible to postulate an important functional role for CD99(MIC2) as it contributes to the malignant phenotype of EFT. In vitro, as well as the first in vivo, experimental evidence suggests that tumor cell expansion and spread can be counteracted by breaking these physiological pathways. Still, we are far from a tailored biological therapy of EFT. Before this goal may be achieved, we must seek further improvements and diversification of today's standard and intensified treatment regimens.