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Introduction Very little is known about the characteristics of mesothelial tumours in the paediatric population. In adults with malignant mesothelioma, the pemetrexed-based regimen with cytoreductive surgery (CRS) is a standard of care in limited tumours, but long-term survival is uncommon. Material and methods The European Cooperative Study Group on Pediatric Rare Tumors (EXPeRT) retrospectively reviewed children, adolescents and young adults (≤21 year) diagnosed with mesothelial tumours treated between 1987 and 2018. Results Thirty-three patients were identified, 15 male and 18 female patients. One patient's exposure to asbestos was documented. Primary tumour was mainly in the peritoneum (23 patients). Histology was multicystic mesothelioma of the peritoneum (MCM) (six patients) or malignant mesothelioma (MM) (27 patients). Among MM, the first-line treatment comprised preoperative chemotherapy (14 cases), surgery only (three cases), chemotherapy only (five cases), adjuvant chemotherapy (three cases) or palliative treatment (two cases). The response rate to cisplatin–pemetrexed was 50% (6/12 cases). CRS with hyperthermic intraperitoneal chemotherapy (CRS-HIPEC) was performed in 19 patients (upfront in three, after neoadjuvant therapy in 12, or after tumour progression in six patients, including three twice). After a median follow-up of 6.7 years (range, 0–20), five-year overall and event-free survivals were 82.3% (95% CI, confidential interval ((CI), 67.8–99.9) and 45.1% (95% CI, 28.4–71.7), respectively. All patients with MCM are alive after surgery (five patients) and CRS-HIPEC (one patient). Conclusions Paediatric mesothelioma is exceptional and seems to be different from its adult counterpart with few asbestos exposures, more peritoneal primary, and a better outcome. The cisplatin–pemetrexed regimen showed promising efficacy. Relapses could be salvaged with active therapy including CRS-HIPEC.

Background Thymomas and thymic carcinomas belong to a group of thymic epithelial tumours arising from the anterior mediastinum and, are extremely rare in children in which no therapeutic guidelines have been established. The aim is to describe paediatric characteristics of these tumours and give some therapeutic indications. Methods Retrospective analysis of clinical data and therapeutic characteristics of paediatric patients less than 18 years with thymic tumours treated between 2000 and 2012 registered in the European Cooperative Study Group for Pediatric Rare Tumors (EXPeRT) database of the cooperating national rare paediatric tumour working groups from France, Italy, Germany and Poland. Results Sixteen children with thymoma, median age 11 years and 20 patients with thymic carcinoma, median age 14 years were enrolled into study. At diagnosis complete primary resection was possible in 11 patients with thymoma and one with thymic carcinoma; resection with microscopic residue was performed in three cases and incomplete resection with macroscopic residue in four patients. Chemotherapy with various regimens was administered to 22 children; 17 of them as neoadjuvant chemotherapy. Eight patients with thymic carcinoma received additional radiotherapy. Seventeen children died (15 thymic carcinoma, two thymoma). Five-year overall survival for patients with thymic carcinoma is 21.0 ± 10.0%. Conclusions This study confirms the possibility to perform European retrospective analysis even in very rare paediatric tumours. Thymic carcinoma is associated with paediatric patients to give a very poor prognosis independently despite multimodal management. Multidisciplinary, multicenter approach and collaboration with adults’ physician are necessary in order to propose homogenous guidelines.

Objective To analyse ovarian Sertoli-Leydig cell tumours (SLCTs) for potential prognostic markers and their use for treatment stratification. Patients Forty-four patients were included. Patients were prospectively reported to the German MAKEI (Maligne Keimzelltumoren) studies ( n =23), French TGM protocols ( n =10), Italian Rare Tumour Project (TREP) registry ( n =6), and the Polish Pediatric Rare Tumour Study group ( n =5). Tumours were classified according to World Health Organisation (WHO) and staged according to International Federation of Gynecological Oncology (FIGO). Results Median age was 13.9 (0.5–17.4) years. All patients underwent resection by tumour enucleation ( n =8), ovariectomy ( n =17), adenectomy isolated ( n =18) or with hysterectomy ( n =1). FIGO-stage: Ia 24pts., Ic 17pts., II/III 3pts. One patient had bilateral tumours. Four patients (stage Ia: 3, stage Ic: 1) developed a metachronous contralateral tumour. Otherwise, all stage Ia patients remained in complete remission. Among 20 patients with incomplete resection or tumour spread (stage Ic–III), eight relapsed, and five patients died. Eleven patients were initially treated with two to sixcycles of cisplatin-based chemotherapy. Of these, seven patients are in continuous remission. Poor histological differentiation was associated with higher relapse rate (5/13) compared to intermediate (3/18) and high differentiation (0/4). Tumours with retiform pattern or heterologous elements showed a high relapse rate, too (5/11). After a median follow-up of 62months, event-free survival is 0.70±0.07, relapse-free survival 0.81±0.06 and overall survival 0.87±0.05. Conclusions Prognosis of SLCTs is determined by stage and histopathologic differentiation. Complete resection with careful avoidance of spillage is a prerequisite of cure. The impact of chemotherapy in incompletely resected and advanced stage tumours remains to be evaluated.

Pancreatoblastoma is a very rare malignant tumour typically occurring in the early years of life. Due to its rarity, standardised diagnostic and therapeutic guidelines are not available for pancreatoblastoma.The newborn cooperative group denominated EXPeRT - European cooperative study group for paediatric rare tumours - combined in a joint analysis of all cases registered between 2000 and 2009 by the national groups of Italy, France, United Kingdom, Poland and Germany.Twenty patients18years old (median age 4years) were analysed: nine had distant metastases at diagnosis. Seventeen patients had tumour resection, at initial or delayed surgery. Eighteen received chemotherapy (response rate 73%), seven received radiotherapy. For the whole series, 5-year event-free survival and overall survival were 58.8% and 79.4%, respectively. Outcome did not correlate with tumour site and size, but was strongly influenced by the feasibility of tumour complete resection.This international study confirms the rarity of the disease, the critical role of surgical resection both as therapy and as a prognostic variable, and the potential efficacy of chemotherapy. The adoption of an intensive multidisciplinary approach is required, as well as the referral to highly experienced centres. Further international cooperation is needed to collect larger series and stimulate biological studies to improve our understanding of the biology and the natural history of PBL.