Very rare tumors are not so rare in children
2024-01-20

The European Journal of Cancer-Paediatric Oncology journal is pleased to present a special issue on very rare tumors of pediatric age. Since the 70th, the international pediatric oncology community has succeeded in developing many effective cooperative protocols on the more common pediatric tumors. On the other side, joining resources and developing international cooperative research had been considered difficult for a group of uncommon diseases, the so-called very rare tumors (VRT) of pediatric age. This definition included tumors that only ever occur in children (such as pleuropulmonary blastoma or pancreatoblastoma) and others that are more common in adults but extremely rare in childhood, such as melanoma and carcinomas (with biological and clinical features that distinguish them from their adult counterpart). These tumors are rare, but taken together they contribute to approximately 10% of all childhood cancers. The situation changed in the early 2000s: various cooperative initiatives have been launched, initially at national level, to improve the knowledge of pediatric VRT and the quality of the treatment of children and adolescents with these uncommon malignancies. Different models have emerged, ranging from national organizations focusing on all VRT occurring in the pediatric age group, to registries dedicated exclusively to certain tumor types (such as the International Pediatric Adrenocortical Tumor Registry IPACTR, the International Pleuropulmonary Blastoma Registry IPPBR, or the registry on NUT-type carcinomas). In Europe, national projects such as the Italian Tumori Rari in Eta Pediatrica (TREP), the Polish Pediatric Rare Tumor Study Group (PPRTSG), the German Seltene Tumor-Erkrankungen in der Paediatrie (STEP) and the Groupe FRAnCais des TUmeurs Rares de l’Enfant (FRaCTurE), have come together in 2008 in the European Cooperative Study Group for Pediatric Rare Tumors (EXPeRT). The EXPeRT - developed under the auspices of the European Society for Paediatric Oncology (SIOPE) - is a model of successful international multilevel organization. It has the two-fold goal to promote research and to provide an advisory service for physicians encountering single clinical cases (for this purpose, an online consultation system was established). EXPeRT initiatives were always characterised by a really multidisciplinary basis (with the involvement of pediatric oncologists and surgeons, together with experts on adult cancers, and specialists in various other branches of medicine, such as endocrinologists or dermatologists). The group has supported the creation of national VRT in other countries, shared data in joint series, developed diagnostic and therapeutic recommendations for the different tumor types, started to establish an international prospective case registry and to plan prospective clinical and biological studies. Notably, the EXPeRT was able to pursue its goals also thanks to the participation to EU-funded collaborative efforts, such as the ExPO-r-Net (European Expert Pediatric Oncology Reference Network for Diagnostics and Treatment) project, the JARC initiative (Joint Action on Rare Cancers) and the PARTNER (Pediatric Rare Tumors Network - European Registry) project. We have learned a lot from the different EXPeRT activities. In particular, we have learned that dealing with rare tumors remains a huge challenge for oncologists worldwide, even in 2023; but we learned also that joining the forces and boost collaborative efforts may help to face the different challenges, from epidemiology and genetic to diagnosis and treatment. With this special issue, we are pleased to invite the readers to see these original articles, that focus on some specific VRT - i.e. salivary gland tumours, melanotic neuroectodermal tumor, olfactory neuroblastoma -, discuss about tumors occurring in cancer predisposition syndromes, talk about biology of VRT and general organization issues, such as the JARC initiative, the virtual consultation system, and - last but not least – the experience of the north-American counterpart, the Children Oncology Group (COG). None