The European Cooperative Study Group for Pediatric Rare Tumors (EXPeRT) is composed of professionals that have dedicated their research activity to increase the scientific knowledge of pediatric very rare tumors and improve the treatment and care of children and adolescents that suffer from these tumors.

Very rare tumors in children are considered those having an incidence of less than 2 cases/million/year and not included in already defined international or national protocols (such as primary liver tumors and germ cell tumors). Some are rare at any age and some are often encountered in the adult population but are exceptional in children.

Univocal diagnostic/therapeutic criteria for these neoplasm do not exist. Moreover, because of their rarity, physicians have often less resources and in some cases less interest in understanding their natural history and developing clinical studies, as well as a biological research.

Additionally, the small number of cases cannot amortize the costs of a specific pharmacologic research and leads to a scarce diffusion of existing information and knowledge.

For all these reasons, rare tumors in pediatric age should be considered as “orphan” diseases.

Examples of very rare tumors in childhood cancer are the following:

• Adrenocortical tumors
• Neuroendocrine Tumors of the lung and of the digestive system
• Gonadal-non germ cell tumors
• Nasopharyngeal carcinoma
• Pancreatic tumors (pancreatoblastoma and Frantz’s tumor)
• Pheochromocytoma and paraganglioma
• Pleuropulmonary blastoma
• Renal carcinoma
• Skin tumors (melanoma)
• Salivary gland tumors
• Thymic tumors
• Thyroid carcinoma
• Epithelial tumors of the digestive system
• Mesothelioma
• Esthesioneuroblastoma
• NUT-midline carcinoma
• Gastrointestinal Stromal Tumor (GIST)

This list is not exhaustive and needs to be continuously updated because newly discovered entities ought to be added.