Very rare tumors (VRTs) account for up to 11% of childhood cancers. Dedicated national groups and registries only exist in some European countries. Pleuropulmonary blastoma (PPB) is a very rare intrathoracic pediatric tumor with a potentially severe prognosis. Due to its rarity, it sometimes goes unrecognized. We investigated PPB diagnostic capability and possible correlations between diagnostic performance and VRT-dedicated activities. The number of cases of PPB registered between 2000 and 2014 at pediatric oncology centers in Europe was compared with the number of expected cases. Data sources included VRT registries, population-based cancer registries, and hospital registries. Data were obtained for 25 countries, grouped into 4 geographical regions. The expected cases were 111, and the observed cases were 129. The observed-to-expected ratio was 1.86 for Northern Europe, 1.33 for Southern Europe, 1.22 for Central Europe, and 0.65 for Eastern Europe. More cases than expected were registered in all countries with an official VRT registry.Conclusion: The number of cases observed is consistent with expectations, but disparities exist across Europe. Difficulties in diagnosing PPB emerged in most Eastern countries. The incidence rate of PPB may be underestimated. The creation of VRT-dedicated groups and a European Registry for VRTs could help to reduce inequalities.What is Known:• Very rare pediatric tumors are often not recognized, despite representing almost 11% of childhood cancers .• Pleuropulmonary blastoma is a rare pediatric tumor with a poor prognosis.What is New:• The ability to diagnose and register pleuropulmonary blastoma varies in Europe.Registries dedicated to very rare pediatric tumors improve the diagnostic rates.• The incidence rate of pleuropulmonary blastoma may currently be underestimated.

Department of Pediatric Hematology and Oncology Children's Hospital Tuebingen Germany

Department of Pediatric Oncology Faculty of Medicine Masaryk University Brno Czech Republic

Klinikum Stuttgart Olgahospital Stuttgart Cancer Center Zentrum für Kinder Jugend und Frauenmedizin Pediatrics 5 Stuttgart Germany

Pediatric Hematology and Oncology Division Department of Women's and Children's Health Padua University Hospital Padua Italy

Pediatric Hematology and Oncology Unit Centro Hospitalar de Sao Joao Porto Portugal

Pediatric Hematology and Oncology Unit Department of Pediatrics Medical University of Gdansk Gdańsk Poland

Pediatric Hematology and Oncology Unit The Queen Silvia Children's Hospital Sahlgrenska University Hospital Goteborg Sweden

Pediatric Hematology Oncology Immunology Unit Angers University Hospital Angers France

Pediatric Hematology Oncology Unit Kaplan Medical Center Rehovot Israel

Pediatric Oncology and Hematology Unit Cruces University Hospital Barakaldo Spain

Pediatric Oncology Unit Aglaia Kyriakou Children's Hospital Athens Greece

Pediatric Oncology Unit Fondazione IRCCS Istituto Nazionale Tumori Milan Italy

Pediatric Oncology Unit Princess Maxima Center for Pediatric Oncology Utrechtx Netherlands

SIREDO Oncology Center Institut Curie Université PSL Paris France

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