Background: Delayed referral and late diagnosis are major contributors to poor childhood cancer survival in low- and middle-income countries (LMICs). Early Warning Signs and Symptoms (EWSS) programs comprise varied mechanisms to support prompt clinical recognition and timely referral of childhood cancer, including clinician training, installing champions, data monitoring, and refining referral pathways. Ensuring both their ongoing delivery and continued clinical benefits requires evidence-based sustainability planning, yet the health system determinants needed to inform this remain understudied. 

Objectives: To explore determinants of sustainability of an EWSS program implemented in Cameroon, a lower-middle-income country, and their evolution over time.   

Methods: We designed a longitudinal qualitative study of an EWSS program implemented in Cameroon in August 2025. Semi-structured interviews were conducted with purposively selected stakeholders in the implementation preparation phase (T1), with follow-up interviews planned 12 months post-implementation of clinician trainings (T2). Interview guides and a deductive coding structure were informed by the Consolidated Framework for Sustainability (CFS) to identify health system determinants of sustainability, with constructs assigned positive (facilitator) or negative (barrier) valence. Findings will be compared across T1 and T2 to examine their evolution over time.  

Results: A total of n=25 interviews were conducted at T1 with national and regional health policymakers, pediatric oncology clinicians, and EWSS program deliverers. Health system determinants, mapped to CFS constructs (square brackets), were identified for sustaining: (i) the delivery of the EWSS core components, including clinician education, local referral champions, and data monitoring, and (ii) the anticipated clinical effectiveness of the EWSS program.  
 
For the continued delivery of EWSS core components, anticipated facilitators included the availability of routinely generated clinical effectiveness data to justify continued education [Credibility of Evidence], involvement of individuals with formal health policy influence [Authority and Influence], and integration with existing pediatric education programs [Structural and Policy Integration]. Anticipated barriers included workforce instability due to redeployments [Human Resources] and data reporting challenges associated with paper-based medical record systems [Practical Workability]. 

For sustained EWSS clinical benefits, anticipated facilitators included a strong organizational and provider-level commitment to early childhood cancer treatment [Urgency and Problem Saliency] and alignment between EWSS and locally recognized patterns of late diagnosis [Problem-Solution Fit]. Anticipated barriers included misalignment with care-seeking norms [Cultural Alignment], high out-of-pocket family costs for cancer diagnostics and treatment, and geographic constraints limiting referral uptake [Socioeconomic Conditions]. Notably, a strong sense of responsibility for improving childhood cancer outcomes [Ownership and Accountability] was perceived as a facilitator for sustaining both delivery and anticipated benefits of the EWSS program. 

Conclusions/Implications for practice or policy: Pre-implementation findings highlight the importance of planning for program sustainability, with distinct considerations required for continued delivery of EWSS core components and the external conditions that facilitate the clinical benefits of early detection. Post-implementation (T2) data collection will explore how determinants of sustainability evolve as the EWSS program transitions from implementation to sustainment. This study advances understanding of health system determinants of sustaining capacity-building innovations in LMICs and provides insights to support the sustained impact of the EWSS program on childhood cancer outcomes in Cameroon.