The European Cooperative Study Group for Pediatric Rare Tumors (EXPeRT) is composed by 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.

The very rare tumors in children are considered those that have 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, 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 reason rare tumors in pediatric age can be considered as “orphan” diseases.

Examples of very rare tumors in childhood are the following

• Adrenocortical tumors
• Carcinoid of the appendix
• Gonadal, non germ cell, tumors
• Nasopharyngeal carcinoma
• Pancreatic tumors
• Pheochromocytoma and paraganglioma
• Pleuropulmonary blastoma
• Renal carcinoma
• Skin tumors like melanoma
• Salivary gland tumors
• Thymic tumors
• Thyroid carcinoma

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