Perceptions and Needs of Stakeholders Regarding MyPal Project’s Electronic Patient-Reported Outcome App: Cross-Sectional Qualitative Focus Group Study - Dimitrios Kyrou; Panos Bonotis; Christine Kakalou; Maria Vasilopoulou; Lydia Scarfò; Marcel Meyerheim; Annette Sander; Tomáš Arpáš; Eleni Kazantzaki; Christos Maramis; Christina Karamanidou (JMIR Cancer)