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Pediatric Oncology

Ewing’s Sarcoma Family of Tumors: Current Management

^a Ste-Justine Hospital, University of Montreal, Montreal, Canada; ^b Children’s Cancer Research Institute, Vienna, Austria; ^c University Children’s Hospital Basel, Basel, Switzerland; ^d Huntsman Cancer Institute & Primary Children’s Medical Center, University of Utah, Salt Lake City, Utah, USA; ^e Department of Radiotherapy, University Hospital Muenster, Münster, Germany; ^f Department of Pathology, University of Pittsburgh School of Medicine and Children’s Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA; ^g University of Muenster, Children’s Hospital, Paediatric Haematology and Oncology, Muenster, Germany

Key Words. Ewing’s sarcoma • Bone cancer • Multimodal therapy • Pediatrics • Adolescents and young adults

Correspondence: Mark Bernstein, M.D., F.R.C.P.(C)., Service of Hematology/Oncology, Ste-Justine Hospital, University of Montreal, 3175 Cote Ste. Catherine Road, Montreal, Quebec, H3T 1C5, Canada. Telephone: 514-345-4969; Fax: 514-345-4792; e-mail: mark. lawrence.bernstein{at}umontreal.ca

Received November 22, 2005; accepted for publication March 16, 2006.

	LEARNING OBJECTIVES

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After completing this course, the reader will be able to:

1. Describe the presentation, differential diagnosis, and prognosis for patients with Ewing’s sarcoma.
   
2. Explain the principles of multidisciplinary management of Ewing’s sarcoma.
   
3. Discuss the late effects of the therapy for Ewing’s sarcoma.
   

	ABSTRACT

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Ewing’s sarcoma is the second most frequent primary bone cancer, with approximately 225 new cases diagnosed each year in patients less than 20 years of age in North America. It is one of the pediatric small round blue cell tumors, characterized by strong membrane expression of CD99 in a chain-mail pattern and negativity for lymphoid (CD45), rhabdomyosarcoma (myogenin, desmin, actin) and neuroblastoma (neurofilament protein) markers. Pathognomonic translocations involving the ews gene on chromosome 22 and an ets-type gene, most commonly the fli1 gene on chromosome 11, are implicated in the great majority of cases. Clinical presentation is usually dominated by local bone pain and a mass. Imaging reveals a technetium pyrophosphate avid lesion that, on plain radiograph, is destructive, diaphyseal and classically causes layered periosteal calcification. Magnetic resonance best defines the extent of the lesion. Biopsy should be undertaken by an experienced orthopedic oncologist. Approximately three quarters of patients have initially localized disease. About two thirds survive disease-free. Management, preferably at a specialist center with a multi-disciplinary team, includes both local control—either surgery, radiation or a combination—and systemic chemotherapy. Chemotherapy includes cyclic combinations, incorporating vincristine, doxorubicin, cyclophosphamide, etoposide, ifosfamide and occasionally actinomycin D. Topotecan in combination with cyclophosphamide has shown preliminary activity. Patients with initially metastatic disease fare less well, with about one quarter surviving. Studies incorporating intensive therapy followed by stem cell infusion show no clear benefit. New approaches include anti-angiogenic therapy, particularly since vascular endothelial growth factor is an apparent downstream target of the ews-fli1 oncogene.

	INTRODUCTION

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Ewing’s sarcoma is the second most frequent primary malignant bone cancer, after osteosarcoma. It is nonetheless an infrequent cancer, with approximately 225 new cases diagnosed in patients less than 20 years of age per year in North America. It is slightly more common in boys (55:45 male:female ratio). The most common age of diagnosis is the second decade of life, although 20%–30% of cases are diagnosed in the first decade. Cases continue to be diagnosed through the third decade, at a lower frequency than in the second decade, and infrequently beyond. In the German European Intergroup Cooperative Ewing Sarcoma Studies (EICESS) series from 1980–1997, approximately 20% were diagnosed in patients >20 years of age. This did not represent, however, a population-based registry. Whites are much more frequently affected than Asians and especially African-Americans, or Africans, in whom the disease is rare [1, 2].

	PRESENTATION

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Locoregional pain is the most common presenting symptom in patients with Ewing’s sarcoma. Pain can be intermittent and variable in intensity. Pain often does not completely disappear during the night [3]. As the majority of Ewing’s sarcoma patients are in their second decade of life and physically active, pain is often mistaken for "bone growth" or injuries resulting from sport or everyday activities. Pain may be accompanied by paresthesia in some cases. Pain as the initial symptom may be followed by a palpable mass. The duration of symptoms prior to the definitive diagnosis can be weeks to months, or rarely even years, with a median of 3–9 months [3–5]. Pain without defined trauma adequate to explain the symptoms, lasting longer than a month, continuing at night, or with any other unusual features should therefore prompt early imaging studies. Slight or moderate fever and other non-specific symptoms are more common in more advanced and/or metastatic stages, affecting about one third of patients [3–6].

Tumor growth eventually leads to a visible or palpable swelling of the affected site. The tumor bulk, however, may be indiscernible for a long time in patients with pelvic, chest wall, or femoral tumors. As Ewing’s sarcoma may arise in virtually any bone and from soft tissue, additional symptoms, depending on the affected site, may vary considerably. Spinal cord compression by a tumor of a vertebral body requires emergency intervention, either laminectomy or chemotherapy or radiotherapy following biopsy. Patients with chest wall or pelvic primaries may experience significant complaints only at a very late stage.

On initial physical examination, tendonitis is a common suspected diagnosis in adolescent or adult patients, while hip inflammation and osteomyelitis are often suspected in younger children [3]. In patients with metastatic disease, nonspecific symptoms such as malaise and fever may resemble symptoms of septicemia. Such patients sometimes also experience loss of appetite and weight. Children under the age of 5 years may thus present a constellation of symptoms similar to those of disseminated neuroblastoma, although Ewing’s sarcoma is uncommon in children <5 years of age.

No blood, serum, or urine test can specifically identify Ewing’s sarcoma. Nonspecific signs of tumor or inflammation may be noted, such as an elevated erythrocyte sedimentation rate, moderate anemia, or leukocytosis. Elevated levels of serum lactate dehydrogenase correlate with tumor burden and, for this reason, with inferior outcome. In contrast to neuroblastoma, serum and urine catecholamine levels are always normal.

Most Ewing’s sarcomas occur in bones. As opposed to osteosarcoma, flat bones of the axial skeleton are relatively more commonly affected, and in long bones, Ewing’s sarcomas, unlike osteosarcomas, tend to arise from the diaphyseal rather than the metaphyseal portion. The most common sites of primary Ewing’s sarcoma are the pelvic bones, the long bones of the lower extremities, and the bones of the chest wall (Fig. 1). Primary metastases in lungs, bone, bone marrow, or combinations thereof are detectable in about 25% of patients. Metastases to lymph nodes or other sites like the liver or central nervous system are rare.

View larger version (44K): [in this window] [in a new window]   Figure 1. Primary tumor sites in Ewing’s tumors. Data based on 1,426 patients from European Intergroup Cooperative Ewing Sarcoma Studies trials. Abbreviation: BM, bone marrow.

View larger version (149K): [in this window] [in a new window]   Figure 2. Magnetic resonance image of a pelvic Ewing’s sarcoma.

	BIOPSY, PATHOLOGY, AND MOLECULAR PATHOLOGY

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Ewing’s sarcoma encompasses tumors with a spectrum of histologic appearances and ultrastructural and immunohistochemical features. Classic Ewing’s sarcoma, as first described by James Ewing in 1921 [12], is composed of a monotonous population of small round cells with high nuclear to cytoplasmic ratios arrayed in sheets (Fig. 3A). The cells have scant, faintly eosinophilic to amphophilic cytoplasm, indistinct cytoplasmic borders, and round nuclei with evenly distributed, finely granular chromatin and inconspicuous nucleoli (Fig. 3B) [13–15]. Mitotic activity is usually low. Cytoplasmic glycogen, which appears as periodic acid-Schiff-positive diastase-digestible granules, is usually present.

View larger version (121K): [in this window] [in a new window]   Figure 3. Histologic and immunohistochemical features of Ewing’s sarcoma/pPNET. (A): Classic Ewing’s sarcoma appears as sheets of monotonous round cells. (Hematoxylin and eosin, original magnification 200x.) (B): The cells have scanty cytoplasm and round nuclei with evenly distributed finely granular chromatin and inconspicuous nucleoli. (Hematoxylin and eosin, original magnification 400x.) (C): Strong, diffuse membrane staining is observed with the O13 monoclonal antibody to p30/32MIC2 (CD99). (Immunoperoxidase, original magnification 400x.)

Because the histologic and immunophenotypic features of Ewing’s sarcoma overlap to varying degrees with the other small round-cell tumors of childhood, an expanded panel of immunohistochemical studies may be necessary to exclude other entities. Like Ewing’s sarcoma, neuroblastoma is immunoreactive for NSE, S-100, and Leu-7, but in contrast to the pPNET variant of Ewing’s sarcoma, it is negative for vimentin and immunoreactive for neurofilament protein. Like Ewing’s sarcoma, lymphoblastic lymphoma is strongly immunoreactive for CD99 in a membrane pattern, but unlike the former, lymphoblastic lymphoma is also immunoreactive for leukocyte common antigen (CD45) and/or TdT and other lymphoid markers. Rhabdomyosarcoma may also be immunoreactive with antibodies to CD99; however, staining is usually focal, weak, and cytoplasmic, and in contradistinction to Ewing’s sarcoma, rhabdomyosarcoma is immunoreactive for myogenin, myoD1, desmin, and actin. The distinction between poorly differentiated small cell synovial sarcoma and poorly differentiated Ewing’s sarcoma may be difficult in some cases. Although synovial sarcoma is immunoreactive for cytokeratin and/or epithelial membrane antigen, poorly differentiated small cell variants may be immunoreactive for CD99 in a membrane pattern and show only focal, weak staining for cytokeratin, thus mimicking poorly differentiated Ewing’s sarcoma.

Molecular genetic studies, using fluorescence in situ hybridization (FISH) and/or reverse transcription-polymerase chain reaction (RT-PCR), are valuable adjuncts for the evaluation of undifferentiated small round-cell tumors of childhood, particularly in cases with indeterminate histologic and/or immunohistochemical features. Detection of characteristic translocations by these methods may allow for definitive diagnosis of Ewing’s sarcoma, rhabdomyosarcoma, and synovial sarcoma [24, 25]. Distinction among these tumors is critical, as their treatments are substantially different.

Ewing’s sarcoma is characterized by a relatively simple karyotype with only a few numerical and structural aberrations. A reciprocal chromosomal translocation between chromosomes 11 and 22, the t(11;22)(q24;q12), is present in about 85% of these tumors [26, 27] and is therefore considered pathognomonic for the disease. In most of the remaining cases, variant translocations are observed always involving chromosomes 22q12 and either 21q22 (10% of Ewing’s sarcomas) or 7p22, 17q12, and 2q36 (<1% of Ewing’s sarcomas each). These variant translocations frequently occur as either complex or interstitial chromosomal rearrangements and are therefore difficult to diagnose by conventional cytogenetics. Additional structural changes affect chromosomes 1 and 16 in about 20% of tumors, most frequently leading to a gain of 1q and a loss of 16q and the formation of a derivative chromosome der(1;16) [28, 29]. Among numerical chromosome changes, trisomy 8 and/or 12 are observed in half and one third of cases, respectively [29, 30]. Deletion of the chromosomal region 9p21 housing the ink4A gene, which has been shown to be homozygously lost in about 25% of Ewing’s sarcoma, remains cytogenetically cryptic in most patients [31, 32]. Loss of heterozygosity at 17p13 with mutation of the remaining p53 tumor suppressor allele is rare (<10% of cases) but, together with homozygous deletions of the ink4A gene, constitutes an unfavorable prognostic factor in this disease [33].

Among recurrent cytogenetic aberrations, the molecular equivalent has been best characterized for the t(11;22)(q24;q12) [34, 35]. The rearrangement results in the translocation of the 3' portion of the friend leukemia virus integration site 1 (fli1) gene from chromosome 11 to the 5' portion of the Ewing’s sarcoma gene ews on chromosome 22 (Fig. 4). In the rare variant translocations, ews is fused to genes closely related to fli1, either erg, e1af/etv4/pea3, etv1/er81, or fev. As a result of the most common, t(11;22)(q24;q12), a chimeric EWS-FLI1 RNA is expressed from the promoter of the rearranged ews gene encoding for a novel fusion protein. The reciprocal translocation product fli1-ews is not expressed and is occasionally lost from Ewing’s sarcoma cells. Using molecular detection methods to monitor the ews-fli1 gene rearrangement, RT-PCR and FISH, the presence of t(11;22)(q24;q12) in 85% of Ewing’s sarcoma has been confirmed and found to correlate with high expression of the cell surface sialoglycoprotein CD99^MIC2 [36, 37].

View larger version (23K): [in this window] [in a new window]   Figure 4. The reciprocal translocation between chromosomes 11 and 22 results in the formation of an ews-fli1 fusion gene on the abnormal chromosome 22 that codes for a chimeric transcription factor with the N-terminal transcriptional regulatory domain deriving from ews and the ets-specific DNA-binding domain derived from fli1.

	STAGING

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Diagnostic staging at presentation must include appropriate search and staging for metastases, which are detected in about 25% of patients (Table 1). The most common metastatic sites are the lungs and the pleural space, the skeletal system, and the bone marrow, or combinations thereof. Locoregional lymph node involvement is rare. Imaging studies should include computed tomography (CT) scan of the chest to document or exclude intrathoracic metastases and 99m-technetium whole-body radionuclide bone scans to search for skeletal metastases. Fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) has recently been proven to be a highly sensitive screening method for the detection of bone metastases in Ewing’s sarcoma, although its exact role in the management of Ewing’s sarcoma remains to be defined. In detecting bone metastases, FDG-PET may be even more sensitive than whole-body MRI scans [54]. Moreover, the initial response to therapy as shown by change in the standard uptake value (SUV), and, perhaps more importantly, the measured SUV after induction chemotherapy, may predict outcome [55].

	CURRENT TREATMENT

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Before the era of chemotherapy, fewer than 10% of patients with Ewing’s sarcoma survived despite the well-known radiosensitivity of this tumor [60, 61]. Patients commonly died of metastases within 2 years, indicating the need for systemic treatment [60]. With the use of modern multimodal therapeutic regimens including combination chemotherapy, surgery, and radiotherapy, cure rates of 50% and more can be achieved [62–76]. The treatment of Ewing’s sarcoma patients worldwide is organized in cooperative trials, aiming to further improve treatment outcome.

Prognostic Features
As discussed in the section on staging, the presence of metastatic disease is the most unfavorable prognostic feature. Those with isolated pulmonary metastases have a slightly better outcome (approximately 30% survive) than those with bone or bone marrow metastases at initial diagnosis (20% or less) [70, 75, 77]. Persistence of Ewing’s sarcoma-specific RNA in bone marrow after treatment may be unfavorable [58, 59]. Children <10 years of age do somewhat better than older patients [75] Size and location of disease are often interrelated, with many larger (>200 ml) lesions located in the pelvis. Patients with such lesions have a lesser chance of survival [73, 75]. The exact translocation type may be of prognostic importance, and the presence of additional cytogenetic changes (see above) may carry unfavorable prognostic weight. The response to initial therapy may also predict outcome [73].

Local Therapy
Cure from Ewing’s sarcoma can only be achieved with both chemotherapy and local control. Current treatment schedules favor primary induction chemotherapy, followed by local therapy and adjuvant chemotherapy. For several decades, radiotherapy was regarded as the standard local treatment modality; contemporary orthopedic surgery, however, is aimed at preserving function and improving limb salvage rates without compromising survival rates [78–81]. In planning the optimal local therapy, an interdisciplinary approach involving experts experienced in this field is essential. The efficacy of this approach was shown in two consecutive European trials by the reduction in local recurrences following the institution of centralized counseling regarding local therapy, including radiation therapy [82]. Local treatment should be individually adapted depending upon the site and size of the tumor, the anatomical structures near the tumor, the patient’s age, and individual preference.

Surgical Treatment of Ewing’s Sarcoma
In general, patients with an isolated, resectable tumor after induction chemotherapy should have their tumors treated with surgery alone. Preoperative radiotherapy may be necessary to avoid an intralesional resection (Table 2). When a negative surgical margin is obtained following preoperative irradiation, local failure rates that are comparable with those achieved with negative margin surgery for more amenable lesions are observed. In Children’s Oncology Group protocols, negative margins are defined as bony margins of at least 1 cm, with a 2- to 5-cm margin recommended. In soft tissue, at least 5 mm in fat or muscle is required, with 2 mm through fascial planes, with the margin being through noninflammatory tissue.

Types of Reconstruction
The main reconstructive options include autogenous bone grafts, structural bone allografts (intercalary or osteoarticular), and metallic endoprosthetics. Allografts and endoprosthetics may also be used as part of a composite reconstruction. Autogenous bone grafts may be vascularized (e.g., fibula). The technique employed is a function of the location of the tumor, age of the patient, and types of adjuvant therapies that will be employed (i.e., chemotherapy and/or radiation). Infection, nonunion, and fracture may complicate the surgery, especially since patients will be receiving continuing chemotherapy and possibly radiotherapy. [83–85].

Generally, after induction (neoadjuvant) chemotherapy, a preoperative follow-up assessment of the tumor must be performed. The response to chemotherapy can be assessed by dynamic MRI. PET and thallium may also provide useful information [55, 86–90]. In certain cases, an individual who was a questionable candidate for limb salvage may be eligible after induction chemotherapy. Patients who remain borderline candidates following induction chemotherapy may be considered for preoperative radiotherapy. If the margins are certain to be inadequate at the preoperative staging evaluation, then amputation is the only available surgical option.

Because Ewing’s sarcomas are radiosensitive, radiation may be used instead of or in addition to surgery.

Radiotherapy

Indications for Radiotherapy
To date, there has been no randomized trial comparing local therapy modalities. Therefore, the question as to which modality, radiotherapy or surgery, is preferred for local therapy in Ewing’s sarcoma has been a matter of debate for some time. From retrospective analyses of several groups, the impression has been that local control is better when surgery is possible [81, 91, 92]. These data are usually confounded by the fact that there is a selection bias favoring patients in whom surgery is possible. Several European and North American collaborative trials have been performed. Overall, local control rates are in the range of 53%–93% with the poorer results usually reported in the earlier series [68, 69, 71, 93, 94].

Definitive Radiotherapy
Patients who receive radiotherapy as the only local therapy modality usually represent an unfavorably selected group of patients. They frequently present with large tumors or tumors in unfavorable locations (e.g., vertebral tumors) or both, making radiotherapy difficult but surgery impossible. In a recent analysis of 1,058 patients with localized Ewing’s sarcoma treated in the EICESS trials, 266 patients had radiotherapy alone. Local or combined local and systemic failures in this subgroup occurred in 26% of patients [81, 91], which was worse than the recurrence rate following surgery with or without radiotherapy (4%–10%). It was not possible to define a subgroup of patients in whom the use of radiotherapy alone achieved the same local control rate as surgery. Even for the favorable subgroup of patients with small extremity tumors, local control was better with surgery than with definitive radiotherapy. Therefore, when marginal or wide resection is possible, surgery should be performed.

Definitive radiotherapy is indicated when only an intralesional resection is possible. Debulking procedures do not improve local control and are associated with additional unnecessary morbidity. In the experience of the European Cooperative Ewing Sarcoma Studies (CESS) and EICESS trials, patients who had an intralesional resection followed by radiotherapy had the same local control rate as patients who had radiotherapy alone [81, 91].

Radiation Dose and Fractionation
In order to control Ewing’s sarcomas, a radiation dose above 40 Gy is necessary. In the St. Jude’s Children’s Research Hospital experience with the use of lower radiation doses, a high rate of local recurrence was observed [93]. A clear dose-response correlation at doses above 40 Gy has not yet been established. For definitive radiotherapy, doses between 55 Gy and 60 Gy, most frequently not exceeding 55.8 Gy, are usually given. When surgery precedes or follows radiotherapy, the doses range between 45 Gy and 55 Gy depending on the individual risk factors (i.e., resection margins and response). It is uncertain whether irradiation of the site of completely resected lesions that demonstrate a poor histologic response is of benefit. European investigators recommend such irradiation, whereas it is not incorporated into North American protocols. There has been no controlled trial addressing this issue.

Usually conventional fractionation with daily fractions of 1.8–2 Gy is given. In the CESS 86 and EICESS 92 trials, hyperfractionated radiotherapy with twice daily 1.6 Gy was also applied; after 22.4 Gy, a 10-day break was scheduled to permit the administration of chemotherapy. There has been no detectable difference in local control between the two different fractionation groups [95].

Target Volume Definition and Treatment Planning
In a randomized trial, the treatment of the whole tumor-bearing compartment showed no better results than radiation to the tumor and an additional safety margin [94]. Therefore, the planning target volume is defined as the initial tumor extent on MRI with an additional longitudinal margin of at least 2–3 cm and lateral margins of 2 cm in long bones. If doses of more than 45 Gy are used, a shrinking field technique is applied. In patients with an axial tumor site, a minimum of a 2-cm safety margin around the initial tumor extent must be employed. In tumors protruding into preformed cavities (i.e., thorax, pelvis) without infiltration, the residual intracavitary tumor volume following chemotherapy is used for treatment planning. Surgically contaminated areas, scars, and drainage sites must be included in the radiation fields. Circumferential irradiation of extremities should be avoided in order to reduce the risk of lymphedema. In growing children, growth plates must be considered. They should either be fully included in the radiation field or they should not be included at all. A dose gradient through the epiphysis results in asymmetric growth and may lead to functional deficits. Similarly, vertebral bodies should either be fully included or spared from the radiation field.

Three-dimensional conformal radiotherapy should be given in patients with Ewing’s sarcoma. In selected cases, that is, in vertebral tumors, intensity-modulated radiotherapy or proton therapy may be beneficial.

Chemotherapy
The first reports of drug treatment of Ewing’s sarcoma stem from the 1960s. In 1962, Sutow and Sullivan [96] and Pinkel [97] independently published reports on the use of cyclophosphamide for Ewing’s sarcoma. With Hustu et al.’s publication on the combination of cyclophosphamide, vincristine, and radiotherapy that resulted in sustained responses in five patients, the era of modern multimodality treatment of Ewing’s sarcoma began [63]. Results of selected phase III studies in Ewing’s sarcoma are listed in Table 3 [5, 67–69, 98–105].

The ongoing EURO-E.W.I.N.G. study includes induction vincristine-ifosfamide-doxorubicin-etoposide for all patients with newly diagnosed Ewing’s sarcoma [109].

Current investigations include the recently completed Children’s Oncology Group study AEWS 0031 that used the strategy of interval compression, with therapy administered every 2 weeks in the experimental arm compared with every 3 weeks in the standard arm. Time-dose intensity of all drugs was thus increased, perhaps interacting in a favorable way with cell cycle kinetics of the malignant cell population. Interval compression was successfully achieved in a preceding limited institution pilot study [110], and preliminary information from the group-wide study supports its feasibility (unpublished data, R. Womer). Efficacy results are not yet available, with the first analysis expected in late 2006. The next Children’s Oncology Group study will incorporate vincristine, topotecan, and cyclophosphamide-containing cycles for a randomized one half of the patients, on the basis of encouraging classic and window phase II studies [111, 112].

Another treatment intensification strategy in Ewing’s sarcoma is high-dose chemotherapy with autologous hematopoietic stem cell rescue (HDT) [113]. Because of the considerable toxicity of this approach, most studies investigate HDT for very high risk patients, most commonly those with metastatic disease at diagnosis, or following recurrence [77, 114–116]. A controlled, randomized study of HDT in Ewing’s sarcoma has recently been undertaken in the framework of the EURO-E.W.I.N.G. 99 studies for patients with large primary tumors locally treated with both surgery and irradiation, or small primary tumors (<200 ml) and an unfavorable histologic or radiologic response to induction chemotherapy (arm R2loc). Accrual is ongoing [109]. Because of the intrinsic risk of using high-dose therapy, such efforts should be strictly limited to the setting of controlled clinical trials [117, 118].

Metastatic Disease
At initial diagnosis, approximately 25% of Ewing’s sarcoma patients present with clinically detectable metastases in the lung and/or in bone and/or in bone marrow. The presence of metastatic disease is the most important adverse prognostic factor [56, 70, 75, 119]. Patients with isolated lung metastases have been shown to have a better prognosis than those with extrapulmonary metastases; however, survival is still disappointing [56, 120]. Bilateral pulmonary irradiation at a dose of 14–20 Gy was reported to improve the outcome of patients with pulmonary disease [121–124]. The Children’s Oncology Group has recently joined the EURO-E.W.I.N.G. randomized study comparing standard therapy including pulmonary irradiation with high-dose therapy using busulfan and melphalan followed by stem cell reinfusion for patients with initially isolated pulmonary metastatic disease (R2pulm) [109].

Solitary or circumscribed bony metastases should be irradiated to doses of 40–50 Gy, in addition to local therapy to the primary site and Ewing’s sarcoma-directed chemotherapy. However, the survival rates of patients with multiple bony metastases are reported to be below 20% [56, 74, 119]. The discouraging results of treatment of metastatic disease has led to more aggressive approaches, including myeloablative high-dose therapy with stem cell rescue. Conclusive results are pending, but preliminary data are discouraging [77, 116].

Alternate approaches include the targeting of the tumor vasculature. Angiogenesis, the generation of new blood vessels, is crucial to the progression of malignant disease[125].These new blood vessels are sensitive to low-dose chemotherapy given over an extended period of time ("metronomic chemotherapy") [126, 127]. In Ewing’s sarcoma, the ews-fli1 oncogene product may function as a promoter for vascular endothelial growth factor. This pathway may thus present a particularly attractive target in Ewing’s sarcoma. The Children’s Oncology Group has recently opened a pilot study, AEWS 02P1, examining the tolerability of a background of low-dose vinblastine and celecoxib [128] therapy incorporated into a standard five-drug regimen (vincristine-doxorubicin-cyclophosphamide alternating with ifosfamide-etoposide).

Recurrent Disease
Superior multimodal therapeutic regimens that combine more intensive systemic treatment with chemotherapy, better surgical approaches, and advanced radiotherapy planning have led to a reduced frequency of recurrent disease, in particular, of local recurrence [67, 129]. Nevertheless, 30%–40% of patients still experience recurrent disease either locally, distantly, or combined, and have a dismal prognosis. Patients with primary metastatic disease have a higher risk for relapse than those with localized disease [70, 129]. The likelihood of long-term survival after recurrence is less than 20%–25% [130–132]. The timing and type of recurrence are important prognostic factors [133]. Patients with early relapse, within the first 2 years following initial diagnosis, have a poorer prognosis, with a 4%–8.5% 5-year survival probability. Those with later recurrence experience a 23%–35% 5-year survival probability [133, 134]. Recurrence may be very late, as compared with most other pediatric and adolescent cancers. A report from the Dana-Farber Cancer Institute described 82 patients initially diagnosed and treated with localized (60 patients) or metastatic (22 patients) Ewing’s sarcoma in 1971–1988. Thirty-one patients survived at least 5 years from diagnosis, of whom five subsequently developed recurrent disease at 5.7, 6.7, 6.9, 9.3, and 17.1 years [135]. Simultaneous local and distant recurrences have been observed to be associated with more aggressive disease with earlier recurrence and poorer outcome [71, 130, 132, 133, 136].

Patients with suspected recurrence should be evaluated appropriately to assess the extent of the local recurrence and the presence of metastatic disease and to plan treatment strategies. The majority of patients with local treatment failure have concomitant distant gross or microscopic disease. Detection of metastases with diagnostic imaging including CT, total body MRI, FDG-PET, and Tc-methylene diphosphonate bone scans is recommended. However, the images may be difficult to interpret because of prior therapy.

There is no established treatment regimen for these patients. Salvage treatment includes multiagent chemotherapy, local control measures with radiotherapy and surgery, or a combination of these as appropriate.

Patients with local recurrence are usually treated with surgery and further chemotherapy [133]. Recurrent distant disease involving the lungs or bones occurs in more than 50% of patients presenting with local recurrence and mandates further chemotherapy [56, 67, 69, 104, 123, 130, 137]. Patients with a single pulmonary nodule appear to benefit from additional whole-lung irradiation and have better outcomes, especially if the recurrence is late, longer than 2 years following the primary diagnosis [123].

Chemotherapy options are limited and dependent on the patient’s prior treatment and possible impaired function of vital organs (e.g., heart and kidneys). Agents that are considered for combination therapy are chosen to potentiate each other’s activity and circumvent the emergence of drug resistance. These have included combinations of topoisomerase I or topoisomerase II inhibitors with alkylating agents and, in addition, several myeloablative high-dose consolidation therapy regimens with and without total body irradiation.

Ifosfamide and etoposide have been shown to be active agents in phase II studies [106–108], although many patients, especially in North America, will already have received these agents as part of their primary therapy. Topotecan in combination with cyclophosphamide produced responses in approximately 35% of patients with recurrent Ewing’s sarcoma [111, 112]. The combination of gemcitabine and docetaxel has been shown to have unexpectedly good activity in leiomyosarcoma and will be investigated in some recurrent sarcomas, including recurrent Ewing’s sarcoma. Both in vitro and anecdotal clinical evidence support this development in the context of a controlled clinical trial. In the pilot study, two patients with Ewing’s sarcoma were among the 35 patients treated. One patient showed a partial response and the other had stable disease [138]. High-dose consolidation therapy with melphalan and etoposide with hyperfractionated total body irradiation with or without carboplatin, followed by autologous stem cell reinfusion, despite initial response, has failed to result in long-term remission in the treatment of early relapse [77, 139, 140]. Results from a hematopoietic stem cell transplantation regimen using combinations of active alkylating agents including busulfan and melphalan seem more encouraging and may improve the prognosis [113, 141]. However, the role of stem cell transplantation in the treatment of patients with recurrent disease is under discussion. Further studies to define the best approach for these patients are needed [77, 113, 134, 139].

Results of treatment of recurrent disease are still unsatisfactory. Whenever possible the patient should be included in organized clinical trials. New drug combinations offering a potential therapeutic benefit are still to be established. Molecular research and a better understanding of Ewing’s sarcoma cell biology with its interplay regulating cell growth, apoptosis, differentiation, genomic integrity, and treatment resistance are needed to enrich the limited portfolio of active agents.

Targeted Therapy
Since the EWS-ETS fusion protein is unique to Ewing’s sarcoma and present in almost all cases, it or critical gene products regulated by the fusion protein represent ideal tumor-specific targets. Experimentally, proof of principle has been obtained by both antisense and RNA interference studies that demonstrated that modulation of EWS-FLI1 expression results in growth inhibition of Ewing’s sarcoma in vitro and in vivo [142–148]. The clinical use of antisense RNA oligonucleotides or small inhibitory RNAs is impeded by the difficulty of efficiently delivering nucleic acids into disseminated tumor cells. One possible method to achieve this goal is the inclusion of oligonucleotides (stabilized as phosphorothioates) into nanocapsules or nanospheres. This approach has been successfully applied to stop Ewing’s sarcoma growth in xenotransplanted nude mice [144, 149].

CD99^MIC2 may represent another promising candidate for targeted therapy in Ewing’s sarcoma. Although neither a ligand for CD99^MIC2 nor the mechanisms by which this antigen is involved in Ewing’s sarcoma are known, in vitro studies on cell lines demonstrated that CD99^MIC2 binding and silencing by specific antibodies induces rapid tumor cell death, enhanced by combination with conventional chemotherapeutic drugs. In vivo studies have been restricted to athymic mice xenografted s.c. with a Ewing’s sarcoma cell line and have indicated reduced Ewing’s sarcoma growth upon anti-CD99^MIC2 treatment [150]. However, there is no direct homolog of CD99^MIC2 in mice and thus toxicity of anti-CD99^MIC2 treatment cannot be assessed in this model. Because of high-level expression of CD99^MIC2 in hematopoietic stem cells and several cell types in the gonads and the pancreas in humans, clinical trials using anti-CD99^MIC2 antibodies have not yet been attempted.

	LATE EFFECTS

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Late effects can be grouped into two major categories: orthopedic outcome, based on the location of the primary tumor and the surgery or radiotherapy used in its therapy, and overall outcome, based on the symptoms initially caused by the disease as well as the entire therapeutic package. Preservation of the hand in patients with upper extremity primaries is associated with a superior functional outcome and better self-image. Orthopedic outcome for patients with lower extremity lesions can be quite satisfactory, even if distal amputation is required. Limb salvage procedures using massive internal prostheses or bone allografts can be complicated by late prosthetic failure or infection, requiring reoperation and, sometimes, delayed amputation.

Radiation therapy can be complicated by growth disturbances of both bone and soft tissue. In addition, irradiation can induce second cancers, most frequently osteosarcoma. This is dose related, with a significantly greater rate at administered doses above 40 Gy. On the other hand, a higher rate of osteosarcoma has been reported after as little as 10 Gy. Moreover, the onset may be late [151–153]. Similarly, chemotherapy has been associated with induced malignancy. There has been a 1%–2% rate of secondary leukemia following a sequence of protocols for Ewing’s sarcoma, usually within 3 years of initial diagnosis. The IESS trial that compared VDC with VDC-IE showed no difference in second malignancies between therapeutic arms, suggesting that, in the dose and schedule employed, the addition of etoposide did not independently increase the risk for a second malignancy [75]. On the other hand, it is notable that arm C of the Children’s Cancer Group–Pediatric Oncology Group Intergroup study INT 0091, designed for patients with disease metastatic at diagnosis, in which very high cumulative doses of ifosfamide (140 g/m²) and cyclophosphamide (17.6 g/m²) were prescribed, also demonstrated a very high rate of therapy-related leukemia, with six patients diagnosed among the 60 treated, a cumulative incidence of approximately 11% (Bhatia S et al., submitted manuscript). Also, exposure to etoposide was linked to the occurrence of a second malignancy in a different series of patients that implicated high-dose therapy even more strongly [154]. There may be a threshold or stepwise effect, with a low rate of induced leukemia with conventional dose treatment, but a much higher rate at the high cumulative doses prescribed in arm C.

Other complications of chemotherapy are agent dependent [155]. Briefly, anthracyclines, including doxorubicin, induce a dose-related cardiomyopathy. Protocol doses are therefore usually limited to less than a lifetime total of 450 mg/m². In addition, administration is often either prolonged over a 48-hour period or, if given as a short i.v. bolus, preceded by the cardioprotectant dexrazoxane, in those jurisdictions in which it is available. Thoracic irradiation that includes the heart can augment the cardiotoxicity of anthracyclines. Doxorubicin is sometimes stopped at the lower cumulative dose of 300 mg/m² if thoracic irradiation is to be given. The alkylating agents cyclophosphamide and ifosfamide are associated with infertility, especially male infertility, so that sperm cryopreservation should be offered to postpubertal boys prior to the institution of chemotherapy. When the technology is better developed, ovarian cryopreservation should similarly be offered to girls. Irradiation is sterilizing. Shielding of the testes and transposition of the ovaries should be considered when appropriate. In addition, ifosfamide can cause a persistent renal tubular electrolyte loss and, less commonly, a decrease in glomerular function, again in a dose-dependent fashion.

Despite these concerns , the overall functioning of survivors of Ewing’s sarcoma is reasonably good [156]. There is frequent need for medical services among survivors, however, so that assuring adequate follow-up and the provision of adequate resources are necessary [157].

	SUMMARY AND CONCLUSIONS

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Ewing’s sarcomas are the second most frequent primary bone cancer, affecting primarily patients in the second and third decades of life. Patients presenting with localized disease have an approximately two thirds chance of being cured. Those whose disease is initially metastatic have a much worse outcome. Those with isolated pulmonary metastases experience an approximately 30% event-free survival rate, whereas those with more widespread disease, usually involving bone or bone marrow, have a less than 20% chance of cure with currently available therapy. Patients whose disease has recurred share this grim outlook. Advances in the biology of Ewing’s sarcoma have led to increased knowledge concerning the underlying molecular basis of the disease, which is as yet insufficient to have led to new therapeutic approaches required to cure those with currently refractory disease, and to cure all with fewer short- and long-term toxicities.

	AUTHORS’ NOTE

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This review article is abridged from chapter 33, Ewing’s sarcoma family of tumors: Ewing’s sarcoma of bone and soft tissue and the peripheral primitive neuroectodermal tumors. In: Pizzo P, Poplack D, eds. Principles and Practice of Pediatric Oncology, Fifth Edition. Philadelphia: Lippincott, Williams and Wilkins, in press, with permission.

	DISCLOSURE OF POTENTIAL CONFLICTS OF INTEREST

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The authors indicate no potential conflicts of interest.

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