The Emerging Triad in Cancer and Aging: Cellular Senescence, Microbiome, and Tumor Microenvironment

Aging is accompanied by a marked increase in cancer incidence and mortality, yet most studies still consider cellular senescence, the tumor microenvironment, and the microbiome as largely separate axes. Here, we propose an integrative triad framework in aging-related cancers in which cellular senescence, tumor microenvironment (conceptualized here as part of a broader tumor microecology), and the microbiome dynamically interact to shape tumor initiation, evolution, and treatment response. We summarize how senescent cells, via context-dependent senescence-associated secretory phenotypes (SASPs), remodel stromal, immune, and metabolic niches in aging hosts and how gut and intratumoral microbiota both induce and are reshaped by senescence. Focusing on colorectal cancer (CRC), hepatocellular carcinoma (HCC) and pancreatic ductal adenocarcinoma (PDAC), together with pan-cancer transcriptomic and microbiome analyses. We highlight disease and subtype-specific patterns in which senescence signatures, immune contexture, and microbial features co-stratify prognosis and therapeutic outcomes, and integrate pan-cancer transcriptomic and microbiome analyses to illustrate shared and divergent triad configurations across tumor types. Finally, we discuss the therapeutic implications of this triad, including timing-dependent use of senolytics and senomorphics, diet and microbiome-targeted interventions, fecal microbiota transplantation (FMT), and the ecological risks of antibiotics, particularly in multimorbid older patients. We argue that triad-informed biomarkers and trial designs integrating senescence, microenvironment, and microbiome readouts will be important for mechanism-based, age-adapted cancer prevention and therapy in older adults, especially those with CRC, HCC, and PDAC.