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Rare Pediatric Tumors
All cancers in children and adolescents are rare. Among them, certain tumors are considered very rare because they are diagnosed in fewer than two children per million each year. They encompass more than fifty different types and can affect almost any organ. Their management requires expert diagnosis, multidisciplinary consultation, and often national or European collaboration.
Rarity is not a diagnosis. It encompasses a wide range of very different diseases, some of which are specific to children, while others are typically seen in adults but are occasionally diagnosed before the age of 18. Their clinical presentation, treatments, and prognosis cannot be summarized by a single rule.
A European definition
The European EXPeRT group defines very rare pediatric tumors as malignant or borderline solid tumors with an annual incidence of fewer than two cases per million children under the age of 18.
Why do these tumors require specialized expertise?
Teams rarely encounter each disease, and traditional clinical trials are difficult to conduct.
Some lesions appear similar under the microscope and require a second review, immunohistochemistry, and molecular testing.
Recommendations are often based on registries, international data sets, and expert consensus.
The same term can encompass differences between children, adolescents, and adults.
Some very rare tumors are more commonly associated with an inherited syndrome.
The strategy can adapt pediatric, adult, and entity-specific recommendations.
Before starting any treatment, confirm the diagnosis
Unplanned surgery or a biopsy can compromise further treatment. Imaging, tissue sampling, and tissue preservation for molecular testing must be coordinated by an expert team.
Which tumors are affected?
The list evolves along with the classifications. The categories listed below illustrate the diversity of situations but do not constitute an exhaustive list.
Carcinomas of the esophagus, stomach, intestine, colon, or rectum; stromal tumors; and certain neuroendocrine tumors.
Solid pseudopapillary tumor, pancreatoblastoma, neuroendocrine tumors, and extremely rare carcinomas.
Adrenal cortical carcinoma, pheochromocytoma, paraganglioma, medullary thyroid carcinoma, and other secretory tumors.
Pleuropulmonary blastoma, lung carcinomas, thymoma, and thymic carcinoma.
Nasopharyngeal carcinoma, esthesioneuroblastoma, carcinomas of the salivary glands, thyroid, larynx, or oral cavity.
Melanoma, skin carcinomas, adnexal tumors, secretory carcinoma of the breast, and other rare tumors.
Pediatric renal carcinoma and other tumors other than nephroblastoma.
Gonadal stromal tumors, carcinomas, and conditions associated with variations in sexual development.
Sarcomas and borderline tumors defined by their histology or a specific molecular abnormality.
NUT tumors, DICER1-associated tumors, rhabdoid tumors, blastomas, and newly defined diseases.
Symptoms
Symptoms depend entirely on the affected organ. A rare tumor may not have any specific symptoms, but certain unusual or persistent symptoms should prompt a visit to the doctor.
A mass in the neck, chest, abdomen, a limb, a breast, or a gonad.
Difficulty swallowing, vomiting, abdominal pain, intestinal obstruction, blood in the stool, or weight loss.
Persistent cough, chest pain, shortness of breath, or repeated infections.
High blood pressure, excessive sweating, hypoglycemia, precocious puberty, virilization, or other endocrine disorders.
Nasal congestion, nosebleeds, hoarseness, difficulty swallowing, a lump, or nerve deficits.
A pigmented lesion that changes, or a nodule that grows, bleeds, or does not heal.
When to Seek Immediate Medical Attention
Respiratory distress, severe difficulty swallowing, an obstruction, significant bleeding, symptomatic hypertension, neurological deficits, sudden pain, or a rapid deterioration in general condition require urgent evaluation.
The Diagnosis
Imaging
Ultrasound, MRI, CT, PET-CT, or functional imaging are selected based on the organ and the diagnostic hypothesis. The goal is to characterize the tumor, prepare for biopsy, and assess for spread.
Pathology
A second review by an expert pathologist is often essential. The microscopic findings are supplemented by immunohistochemistry and, depending on the specific tumor type, by chromosomal or molecular analyses.
Molecular Biology
DNA or RNA sequencing can confirm a disease, identify a gene fusion, distinguish between similar entities, and sometimes reveal a therapeutic target. However, a potentially targetable abnormality does not automatically lead to treatment.
Constitutional genetics
An oncogenetic consultation is considered when the tumor type, age, multifocality, or personal and family history suggest a predisposition. The results may alter the follow-up care for the child and, in some cases, for their family.
It may be helpful to consult both a pediatrician and an adult physician
Some very rare childhood tumors are more similar to adult cancers. In such cases, diagnosis and treatment can benefit from collaboration between experts in both fields, without automatically applying adult treatment practices.
Treatments
There is no single treatment that applies to all rare tumors. The treatment strategy depends on the diagnosis, age, stage, location, the feasibility of complete surgery, the expected response to treatment, and any molecular abnormalities.
Surgery
Surgery is the primary treatment for many localized tumors. It must be performed by a team familiar with the specific tumor type and the affected organ, with the goal of achieving complete resection while preserving function.
Chemotherapy
Its role varies greatly. Certain blastomas, lymphomas, or sarcomas are sensitive to it, while many pediatric carcinomas show little response. Treatment regimens may be based on pediatric protocols or adapted from adult data.
Radiation therapy
It can complement surgery, treat an inoperable tumor, or control symptoms. In children, the decision takes particular account of tissue growth and the risk of late effects.
Targeted Therapies
A fusion or mutation involving ALK, NTRK, RET, BRAF, or another signaling pathway may sometimes guide drug selection. Its use depends on the diagnosis, level of evidence, age, regulatory approval, and access to a clinical trial.
Hormonal and Metabolic Therapies
Certain secretory tumors require monitoring of hormonal effects before and during tumor treatment.
Surveillance
For certain borderline or slow-growing tumors, structured monitoring can prevent unnecessary or debilitating treatment.
No standard treatment does not mean there is no strategy
The decision is based on available recommendations, international data, collective expertise, and the preferences of the patient and their family. It is reassessed as the situation evolves.
A Look at Some Families
This term has largely replaced “carcinoid.” Most well-differentiated appendiceal tumors discovered after appendectomy have a favorable prognosis, but management depends on specific pathological criteria and not on size alone.
They are often associated with a genetic predisposition in children. Hormone and blood pressure monitoring is performed prior to surgery.
Steroid secretion is common in children. The possibility of a genetic predisposition, particularly related to TP53, should be discussed.
This rare lung tumor in children is often associated with DICER1 syndrome, which warrants genetic testing.
A genetic predisposition, polyposis, or inflammatory disease may be investigated. Management involves a combination of adult and pediatric gastroenterology expertise.
It differs from nephroblastoma. Surgery is central to treatment, and molecular characterization can guide the classification and treatment of advanced forms.
European Research, Databases, and Recommendations
The European EXPeRT group develops harmonized recommendations, organizes expert consultations, and supports registries dedicated to very rare tumors. Guidelines are available for several conditions, including adrenocortical tumors, pleuropulmonary blastoma, nasopharyngeal carcinoma, thymic tumors, and appendiceal neuroendocrine tumors.
The PARTNER registry prospectively collects information on these diseases in Europe. The March 2026 European publication also describes a virtual consultation and a transatlantic platform aimed at harmonizing data and preparing for future studies.
Why Registers Are Essential
When a randomized trial is not feasible, standardized data collection helps us better understand the natural history of a condition, compare treatment strategies, and develop recommendations.
Precision Medicine and Clinical Trials
Precision medicine can be particularly useful when a very rare tumor carries an abnormality that defines the disease or serves as a therapeutic target. However, promising results obtained in small groups must be confirmed and do not automatically constitute a new standard of care.
Open-label trials are evolving rapidly. Their availability depends on the diagnosis, age, molecular abnormality, prior treatments, and clinical status. The website should link to a dynamic module rather than publish a static list.
Long-term follow-up
Follow-up care is designed to detect recurrence and manage long-term effects. It is tailored to the specific organ, the type of surgery, medications, areas treated with radiation, and any potential predisposition.
Monitoring of digestive, respiratory, endocrine, renal, neurological, or functional systems, depending on the location.
Treatments can affect growth, hormones, and fertility.
A specific screening program may be recommended when a genetic syndrome is identified.
Schooling, academic studies, physical activity, pain management, nutrition, and psychological support are all integrated into the program.
Care must remain coordinated during the transition from the pediatric unit to the adult teams.
The risk depends on genetic predisposition and treatment and is part of personalized care.
Patient Care at Gustave Roussy
The Department of Pediatric and Adolescent Oncology coordinates patient care with teams specializing in imaging, pathology, molecular biology, genetics, surgery, radiation therapy, nuclear medicine, endocrinology, and supportive care. Very rare cases may be discussed with adult specialists, national networks, and European groups.
When the disease recurs or is difficult to treat, in-depth molecular characterization and access to a clinical trial may be discussed. Eligibility depends on the exact diagnosis and the protocol criteria.
Coordinated expertise, sometimes across multiple sites
Certain procedures or tests are performed in collaboration with partner institutions. Gustave Roussy continues to coordinate oncology care and lead multidisciplinary discussions regarding the patient’s care pathway.
Key Points
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A precise definition
A very rare pediatric tumor occurs in fewer than two children per million per year.
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More than fifty types
Their origins, progression, and treatments vary greatly.
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An expert diagnosis
A pathological review and molecular analyses are often necessary.
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A Tailored Strategy
Pediatric, adult, and international data are discussed together.
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Genetics Can Play a Role
For certain conditions, it makes sense to screen for predisposition.
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Collaboration Advances Care
Networks, registries, EXPeRT guidelines, and clinical trials help build knowledge.