BACKGROUND: Palliative care is crucial for patients with life-threatening and serious diseases such as cancer, as it addresses their physical, psychosocial, and spiritual needs. Hematological malignancies significantly contribute to global cancer cases, impacting both older adults and children. To meet the increasing demand for palliative care, electronic patient-reported outcome (ePRO) interventions offer valuable insights into patient monitoring and treatment decision-making. The MyPal project developed a digital ePRO solution to improve palliative care by enabling structured symptom reporting and promoting physician-patient communication. OBJECTIVE: This study aims to explore the perceptions, opinions, and needs of adult and pediatric patients with cancer, caregivers, and health care professionals (HCPs) regarding low-fidelity versions of the MyPal project's digital solution, which is designed to improve palliative cancer care. METHODS: A qualitative, cross-sectional study was conducted using 12 prepilot focus groups (FGs) across 4 European countries (Greece, Italy, Germany, and the Czech Republic) at participating hospitals and research centers. The FGs, held in person, included 61 participants, including 27 (44%) adult patients with chronic lymphocytic leukemia or myelodysplastic syndromes, 19 (31%) children with hematological malignancies or solid tumors and their parents, and 15 (25%) HCPs specializing in oncology and palliative care. A semistructured discussion guide, informed by vignettes and user personas, was used to facilitate discussions. Sessions were audio recorded, transcribed, and analyzed using thematic analysis to identify and extract themes and subthemes from the FG discussions. RESULTS: Three main themes emerged from the FG discussions. The first theme, improved care, showcased the project's potential to enhance health care through patient-reported measures by improving symptom monitoring, streamlining decision-making, and strengthening physician-patient communication. Patients and caregivers valued the ability to report symptoms remotely, reducing unnecessary hospital visits, while HCPs appreciated having structured patient data to guide treatment. The second theme, digital communication framework, revealed that while participants recognized the benefits of digital tools, they had concerns about data security, privacy, and clarity regarding communication protocols. Questions emerged about how and when HCPs would review and respond to patient-reported data. In the third theme, applicability for use in health care, participants emphasized the importance of the system's ease of use, particularly for older patients and young children. Concerns were raised about the potential intrusiveness of the system, particularly regarding notification frequency and the impact on daily life. HCPs highlighted workload challenges, suggesting the need for a structured alert system to prioritize urgent cases. CONCLUSIONS: Our findings indicate that ePRO-based interventions such as MyPal can improve palliative care by facilitating communication and patient monitoring. However, addressing privacy concerns, optimizing usability for diverse populations, and ensuring seamless integration into clinical workflows are critical for successful adoption. Insights from this study will inform future development and optimization of eHealth interventions in palliative care.