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Article History

Received: 7 November 2025

Accepted: 5 December 2025

First Online: 20 January 2026

Declarations

:

: Dimosthenis Andreou reports payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from PharmaMar GmbH and participation on an Advisory Board for SpringWorks Therapeutics. Stefan Bielack reports consulting fees from SERB SAS (Advisory Board, payment to himself), consulting fees from Atheneum Partners GmbH (payment to himself), and consulting fees from Medicys Healthcare Fieldwork Experts (payment to himself); and payment for expert testimony from Zschimmer & Schwarz Mohsdorf GmbH & Co. KG (payment to himself). Stefanie Hecker-Nolting reports support for the present manuscript from Förderkreis Krebskranke Kinder e.V. Stuttgart, Germany (Charity foundation, funding); grants or contracts from Deutsche Kinderkrebsstiftung, Bonn, Germany (Charity foundation, grant for COSS); leadership role in FOSTER (Fight Osteosarcoma through European Research), member of Executive Committee (EC), Lead WP3 (unpaid); leadership role in COSS (Cooperative Osteosarcoma Study Group) (head of study group); and leadership role in HIBISCUS (member of EC) Thekla von Kalle reports leadership or fiduciary role in other board, society, committee or advocacy group, paid or unpaid for GPR—German Speaking Society of Paediatric Radiology (President, no payment), and ESPR—European Soc. of Paediatric radiology (Member of Oncology task force, no payment). Thomas Kühne reports support for the present manuscript from IPSEN (honoraria). Peter Reichardt reports consulting fees from Bayer (to institution), GSK (to institution), PharmaMar (to institution), and Boehringer Ingelheim (to institution); payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from PharmaMar (to institution) and Boehringer Ingelheim (to institution); and leadership or fiduciary role in other board, society, committee or advocacy group, paid or unpaid as chairman of the German Sarcoma Foundation. Reinhard Windhager reports consulting fees from Johnson & Johnson Medical Limited and consulting fees from Stryker European Operations Limited; and other financial or non-financial interests from De Puy Synthes (Product Development Agreement with Medical University Vienna), other financial or non-financial interests from Johnson & Johnson Medical Limited (Life Case Obsevation Agreement with Medical University Vienna), and other financial or non-financial interests from Johnson & Johnson Medical Limited (Educational Agreement: MedUni with Medical University Vienna). Daniel Baumhoer, Claudia Blattmann, Godehard Friedel, Birgit Fröhlich, Semi Ben Harrabi, Leo Kager Torsten Kessler, Matthias Kevric, Antonia Knoll, and Benjamin Sorg report no conflicts of interest to disclose.

: The studies and registries which form the basis of this work were approved by Ethik-Kommission bei der Ärztekammer Hamburg nos. 500, 1147; Ethikkommission der Ärztekammer Westfalen-Lippe und der Westfälischen-Wilhelms Universität nos. 182/98 Biel2, 4IV Bie 2, 4 I Bielack, 5 V. Bielack; and Ethik-Kommission an der Medizinischen Fakultät der Eberhard-Karls-Universität und am Universitätsklinikum Tübingen no. 5 V Bielack.

: Informed consent was obtained from all patients and/or legal guardians, whichever appropriate, before enrolment into the COSS-database.

: Not applicable.

: Not applicable.