A system dynamics modelling protocol to evaluate the impact of a health financing mechanism for breast cancer pharmacotherapies in Malaysia

INTRODUCTION: The rising cost of targeted breast cancer therapies challenges financial sustainability and equitable access in dual-tier health systems. In Malaysia, public cancer care is highly subsidized but budget constrained, shifting patients toward private services that are typically financed through out-of-pocket payments, private health insurance or employer-sponsored insurance. Rakan KKM (MOH's Friend) is a fee-for service initiative in selected public hospitals designed to provide lower-cost private care, with revenues reinvested into the public system. However, its financial implications for breast cancer pharmacotherapy remain uncertain. This manuscript presents a methodological protocol for a system dynamics (SD) model developed to evaluate the financial implications of Rakan KKM for breast cancer pharmacotherapy in Malaysia. METHODOLOGY: A system dynamics model has been developed to model breast cancer disease progression across stages and patient movement between public, private and Rakan KKM care settings, integrating associated healthcare expenditures and revenue flows from the perspective of the Ministry of Health. An influence diagram was constructed through stakeholder engagement to identify key feedback mechanisms influencing access, affordability and system sustainability. Model parameterisation is complete, using national epidemiological data, published registries data, national drug acquisition cost estimates and expert elicitation from oncology clinicians and pharmacists. This protocol details the simulation framework where a status quo scenario is compared against intervention scenarios over a 10-year horizon. One-way sensitivity analysis and monte-carlo simulations address parameter and clinical uncertainties, while scenario analyses guided by the Diffusion of Innovation framework examine alternative uptake rates and capacity constraints. CONCLUSION: This protocol describes a transparent and adaptable SD modelling approach to assess the fiscal sustainability of financing high-cost breast cancer therapies in mixed public-private systems by projecting how patient switching influences pharmacotherapy expenditure and the net resources potentially available to support public service investment through Rakan KKM.