Targeting tumor transition windows.

Tumor heterogeneity and cellular plasticity are major drivers of therapeutic failure across many cancer types. While precision oncology has largely focused on static genomic alterations, growing evidence indicates that tumors behave as dynamic biological systems that continuously adapt during treatment. Tumor cell populations can transition between distinct functional states under therapeutic pressure, including transient drug-tolerant phenotypes that may precede stabilization of genetically or epigenetically resistant clones. These transitions are shaped by mechanisms such as epigenetic reprogramming, stress-response signaling, metabolic rewiring, and microenvironmental interactions. This review synthesizes findings from tumor plasticity, drug-tolerant persister biology, therapy-induced vulnerabilities, clonal evolution, and adaptive therapy to examine how temporal tumor dynamics influence treatment response. Emerging evidence suggests that some tumors may pass through short-lived phases of cellular instability during therapy in which molecular dependencies, stress-response programs, or adaptive survival states are altered before resistance becomes genetically or epigenetically stabilized. However, such transition states should be considered therapeutically actionable only when linked to functional evidence of altered drug sensitivity, pathway dependence, immune susceptibility, or clinical response. Advances in single-cell transcriptomics, epigenomic profiling, serial circulating tumor deoxyribonucleic acid (ctDNA)/cfDNA analysis, multi-omics integration, and dynamic imaging are enabling longitudinal monitoring of tumor state transitions and may facilitate identification of transient biological states preceding stable resistance. Integrating temporal tumor biology with therapeutic sequencing strategies, adaptive treatment schedules, and biomarker-guided monitoring may therefore help test whether specific adaptive states can be therapeutically exploited and may refine precision oncology approaches.