Bridging Data Silos in Oncology with Modular Software for Federated Analysis on Fast Healthcare Interoperability Resources: Multisite Implementation Study - Jasmin Ziegler; Marcel Pascal Erpenbeck; Timo Fuchs; Anna Saibold; Paul-Christian Volkmer; Guenter Schmidt; Johanna Eicher; Peter Pallaoro; Renata De Souza Falguera; Fabio Aubele; Marlien Hagedorn; Ekaterina Vansovich; et al. (Journal of Medical Internet Research)