Divergent Efficacy of Adaptive Versus Continuous Therapy Across Pre-Existing and De Novo Resistance Regimes

Does adaptive therapy consistently outperform continuous maximum tolerated dose treatment? Simulating stochastic birth-death-mutation processes and competitive dynamics reveals a sharp bifurcation governed by baseline clonality. Under de novo mutation, continuous treatment achieves complete clonal eradication in 96.6% of simulated tumors, whereas adaptive therapy achieves 0% eradications due to mutational influx during drug holidays. Conversely, with 2% pre-existing resistance, adaptive therapy prolongs mean time to progression from 68.6 days to 74.8 days while reducing cumulative drug exposure by 18.1%. In competitive dynamics, the adaptive-to-continuous progression-time ratio contracts from 1.11 under a 20% fitness cost to 1.09 under neutral resistance. Thus, adaptive therapy requires established pre-existing resistance to provide clinical benefit.