In Hong Kong, the incidence of paediatric cancer has been increasing in the past few years, from 180 new cancer cases in 2017 to 196 cases in 2019. The average 5-year survival rate for paediatric cancer patients is approximately 85% due to recent advances in cancer treatments. The success of these treatments has resulted in a rapid growth in the population of paediatric cancer survivors globally. This population now has an average lifespan of 72 years. Despite the improved survival rate, the high toxicity and low specificity of cancer treatment given at an early age induce a myriad of deleterious late effects that have a detrimental impact on survivors' physical and psychosocial well-being. Therefore, children who have completed cancer treatment require ongoing monitoring for cancer progression and survivorship care as early as possible to manage the symptoms induced by the invasive treatment. Symptom management in paediatric oncology nursing is becoming increasingly important due to the complex treatment modalities. The benefits of effective symptom management, particularly improvements in physical functioning and reduced psychological distress, are exponential for children being treated for cancer and their caregivers throughout the cancer trajectory.

Paediatric oncology patients receive close monitoring of their somatic symptoms during their hospital stay, but there is a paucity of symptom management for children who have completed treatment and are at the early stage of survivorship. During the transition from hospital stay to home care, children and their caregivers may experience significant psychological distress due to their concerns about the child's health and uncertainties about coping with the potential symptom burden or cancer recurrence. During the first year after completing cancer treatment, many side effects related to the cancer or its treatment may persist, and other late effects may also develop. The unmet needs for symptom monitoring and management for paediatric cancer survivors, particularly those in the early stage of survivorship, warrant immediate attention from healthcare professionals. It is imperative for healthcare professionals to engage in the rigorous planning, development, and implementation of appropriate interventions to support symptom management for children in the early stage of cancer survivorship and their caregivers. These interventions should be implemented at discharge to manage patient-reported symptoms and improve the children's QoL and survival rate.

Given the high utilisation of mobile technologies, integrating mobile technologies into current cancer survivorship care may be a promising and flexible approach for symptom management for children in the early stage of cancer survivorship and their caregivers. Digital health interventions have been shown to be effective at improving patient-reported outcomes in various patient populations, but there is a lack of such an intervention for paediatric cancer survivors and their caregivers to ameliorate their symptom burden in their local contexts (e.g., at home). The proposed study aims to develop a symptom management mHealth app to support children in the early stage of cancer survivorship and their caregivers and to evaluate its usability, feasibility, acceptability, and efficacy.