The goal of this randomized controlled trial is to examine the efficacy of the mHealth app in improving symptoms experienced by children in the early stage of cancer survivorship, including physical function, anxiety, depressive symptoms, fatigue, peer relationships, and pain interference, and at improving the quality of life (QoL) of the children's primary caregivers

The main question it aims to answer is whether survivors who receive the symptom management mHealth app intervention will report improved symptoms, i.e., improved physical function; lower levels of anxiety, depressive symptoms, and fatigue; better peer relationships; and lower pain interference 3 months after starting the intervention. Additionally, we hypothesized that the primary caregivers (either the mother or father) would report an improved QoL 3 months after starting the intervention.

Participants in the intervention group will use the mHealth app for 12 weeks with personalised nurse support via interactive communication technologies. They are required to complete questionnaires at baseline (during medical follow-up), 1, 2, and 3 months (via electronic-based systems in the mobile app) Besides, semi-structured interviews and will be conducted to examine the usability, feasibility, and acceptability of the intervention.

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 [1]. The average 5-year survival rate for paediatric cancer patients is approximately 85% due to recent advances in cancer treatments [2]. 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 [2]. 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 [3-5]. 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 [3]. 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.

Inclusion Criteria:

Chinese paediatric cancer survivors will be included if they

• are aged 9 to 16 years,
• are able to read Chinese and communicate in Chinese,
• have completed active cancer treatment (within the previous 2 years), as early symptom management support is crucial to reduce the symptom burden in survivors and their caregivers throughout their survivorship, and
• have a smartphone or tablet and are willing to install the mHealth app.

The primary caregiver of the paediatric cancer survivors (either the mother or father)

• are able to read Chinese and communicate in Chinese, and
• have a smartphone or tablet and are willing to install the mHealth app with their children surviving cancer.

Exclusion Criteria:

Chinese paediatric cancer survivors will be excluded if they

• have cognitive impairments or psychiatric illnesses
• are currently participating in other symptom management studies, or
• have evidence of secondary malignancy or recurrence

The primary caregivers of the paediatric cancer survivors (either the mother or father) will be excluded if they have cognitive impairments or psychiatric illnesses.