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Soft Tissue Sarcomas (STS)
Soft tissue sarcomas are rare cancers that develop in the body’s supporting tissues, including muscles, fat, fibrous tissues, blood vessels, and nerve sheaths. In children and adolescents, they encompass a wide range of diseases that differ significantly in terms of diagnosis, behavior, and response to treatment.
Soft tissue sarcomas account for about 6% of childhood cancers. Rhabdomyosarcoma is the most common type among children aged 0 to 14. The other forms, often grouped under the term “non-rhabdomyosarcomatous sarcomas,” constitute a highly heterogeneous group.
An increasing mass must be investigated
Most soft-tissue masses in children are benign. However, a persistent, deep, hard, immobile, painful, or enlarging mass should prompt imaging and consultation with a specialist.
The Main Types
The most common soft tissue sarcoma in children. Treatment typically combines chemotherapy with local control.
A tumor characterized by an SS18::SSX fusion. Despite its name, it does not necessarily originate in a joint.
A tumor in infants that is often associated with an NTRK fusion, most commonly ETV6::NTRK3.
A tumor that may involve an ALK fusion, a ROS1 fusion, or another kinase abnormality.
A sarcoma that develops from the sheath of a nerve, sometimes associated with type 1 neurofibromatosis.
A rare sarcoma, often associated with a loss of SMARCB1 or INI1.
Angiosarcoma and epithelioid hemangioendothelioma are distinct and very rare conditions.
Liposarcoma, leiomyosarcoma, clear-cell sarcoma, and undifferentiated sarcomas require specialized expertise.
Why does the disease occur?
In most cases, no cause is identified. The disease is not related to diet, lifestyle, or psychological factors. Certain predisposing conditions, such as Li-Fraumeni syndrome or type 1 neurofibromatosis, increase the risk. Previous radiation therapy may also play a role several years later.
Symptoms
The most common symptom is a mass that grows in size, sometimes without causing pain. The symptoms then depend on the location of the mass and the structures it compresses.
Swelling, pain, difficulty moving, or nerve compression.
Obstruction, bleeding, or problems with vision, hearing, or swallowing.
Cough, pain, shortness of breath, or a mass on the chest wall.
Pain, constipation, urinary problems, or a deep mass.
A persistent lump, or a lesion that grows, changes in appearance, or bleeds.
Fatigue, fever, or weight loss are possible but nonspecific.
When to Seek Immediate Medical Attention
A rapidly growing mass, weakness in a limb, neurological signs, difficulty breathing, urinary or gastrointestinal obstruction, or significant bleeding require prompt evaluation.
The Diagnosis
Imaging Before a Biopsy
Ultrasound can guide the evaluation of a superficial mass. MRI is the gold standard for deep masses and assesses their relationship to muscles, nerves, blood vessels, and joints. CT scans and, in some cases, PET-CT scans are used to complete the workup, depending on the location and subtype.
A Planned Biopsy
The biopsy must be coordinated with the surgical team. The biopsy path must be able to be included within the planned resection. An unplanned excision may require a more extensive revision and compromise local control.
Molecular analysis
The diagnosis combines histology, immunohistochemistry, and, if necessary, DNA and RNA analyses. RNA sequencing detects gene fusions, among other things. These results can confirm a specific entity, determine its risk level, or identify a therapeutic target.
A high-quality sample is essential
The biopsy must provide sufficient tissue for diagnosis and molecular testing. Unless there is an exceptional emergency, treatment begins after the tumor has been adequately characterized.
Assessment of the extent of the disease and prognosis
The evaluation assesses for local, lymph node, or metastatic spread. The lungs are a common site for several types of sarcomas, but the necessary tests vary depending on the specific type. The prognosis depends on the precise diagnosis, grade, size, location, the possibility of complete resection, and the presence of metastases.
Treatments
The treatment strategy is discussed during a specialized multidisciplinary team meeting and depends on the subtype, age, location, grade, extent, and expected functional consequences.
Surgery
Surgery is the primary treatment for many localized sarcomas. The goal is en bloc resection with adequate margins, without tumor rupture, followed by reconstruction if necessary.
Chemotherapy
Its role varies significantly. It is essential for rhabdomyosarcoma, but several other sarcomas are not very responsive to it. It may be recommended for certain high-risk, metastatic, or recurrent forms.
Radiation Therapy
It can complement surgery when the local risk is high or be used if complete resection is impossible. Modern techniques aim to minimize exposure of healthy tissue.
Targeted Therapies
TRK inhibitors may be used in certain tumors harboring an NTRK fusion. ALK inhibitors may be recommended for certain ALK-positive inflammatory myofibroblastic tumors.
A molecular abnormality is not always enough
A target must be interpreted in conjunction with the diagnosis, stage, and clinical data. Targeted therapy is not automatically indicated as soon as an abnormality is detected.
In the event of a relapse or metastatic disease
A new biopsy and molecular analysis may be considered. The treatment strategy may include surgery for certain lesions, radiation therapy, chemotherapy, targeted therapy, or participation in a clinical trial. It is tailored to each patient based on the subtype, time to relapse, and previous treatments received.
Research and Precision Medicine
The research aims to better classify these rare tumors, identify biomarkers, and guide patients toward appropriate treatments. At Gustave Roussy, the TargetSWITCH project is studying the molecular diversity of epithelioid sarcomas. The EZHiSWITCH academic trial is evaluating valemetostat in several tumors with SMARCB1 or SMARCA4 loss, including certain epithelioid sarcomas.
An essay is not a standard
Experimental drugs are offered only to patients who meet the protocol criteria, after they have been informed and have given their consent. Their benefits and risks are still being evaluated.
Long-term follow-up
Follow-up care is designed to detect recurrence and monitor the effects of the tumor and treatments. It is tailored to the subtype, location, surgery, radiation therapy, and medications received.
Rehabilitation, prosthetics, and postoperative follow-up support the recovery process.
Surgery or radiation therapy can affect the growth of a limb or tissue.
Follow-up depends on the chemotherapy treatments received.
Stiffness, fibrosis, growth abnormalities, and the risk of a second cancer are monitored.
Reconstruction, psychological support, and social services may be necessary.
Education, academic studies, adapted physical activity, pain management, and nutrition are all integrated into the program.
Patient Care at Gustave Roussy
Gustave Roussy is one of the coordinating centers of the national NETSARC+ network. The diagnosis may be reviewed by an expert, and the case is discussed at the sarcoma multidisciplinary team (MDT) meeting. For children and adolescents, the Department of Pediatric and Adolescent Oncology coordinates the care pathway with the teams in imaging, pathology, molecular biology, surgery, radiation therapy, and supportive care.
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Very Different Diseases
The specific name and molecular profile determine the strategy.
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A growing mass should be investigated
Pain is not always present.
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A Scheduled Biopsy
Its location will influence the future surgery.
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Surgery often plays a central role
Chemotherapy and radiation therapy play a varying role
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Molecular biology is transforming diagnosis
NTRK, ALK, ROS1, or SS18::SSX fusions can confirm a specific condition or guide treatment.
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National Expertise
The diagnosis and strategy are discussed in NETSARC+.