Senescence in cancer: Hallmarks, paradoxes, and therapeutic promise

Cellular senescence is a conserved stress-responsive program defined by durable proliferative arrest and extensive remodeling of chromatin, metabolism, intercellular signaling, and immune interactions. Initially described as a barrier to unlimited cell division, senescence is now recognized as a pleiotropic and heterogeneous biological process with roles in development, tissue repair, immune surveillance, tumor suppression, aging, fibrosis, and cancer progression. Despite its broad relevance, senescence remains challenging to define operationally, as its molecular features, functional outputs, and physiological consequences vary across cell types, tissues, and stimuli. This review summarizes core hallmarks of senescence while synthesizing how these features are differentially engaged, diversified, and repurposed across biological contexts. Focusing on cancer, we discuss how senescence influences tumor initiation, evolution, and therapeutic response through both cell-intrinsic and microenvironmental mechanisms. We further evaluate emerging strategies to therapeutically modulate senescence, highlighting both opportunities and unresolved challenges for precision intervention.