Bacterial-based cancer therapy: mechanisms and therapeutic advances

Targeted cancer therapies increasingly require platforms that can penetrate poorly perfused tumor regions while minimizing systemic toxicity. Bacteria, owing to their intrinsic tumor tropism, genetic programmability, and immunostimulatory properties, have re-emerged as versatile anticancer agents, ranging from attenuated tumor-colonizing strains to highly engineered "living therapeutics." In this review, we synthesize the mechanistic foundations and therapeutic advances of bacterial-based cancer therapy through four major themes. First, we examine foundational mechanisms, including tumor-selective colonization, direct oncolysis and cytotoxicity, activation of innate and adaptive immunity, and remodeling of the tumor microenvironment. Second, we discuss engineering strategies that enable controllable delivery of therapeutic payloads, such as cytokines, antibodies and nanobodies, enzyme-prodrug systems, toxins, and nucleic-acid therapeutics, while also improving biosafety and biocontainment. Third, we evaluate combination strategies integrating bacteria with chemotherapy, radiotherapy, phototherapy, and immunotherapy, with emphasis on how bacteria complement conventional modalities by targeting hypoxic, necrotic, and immunologically refractory tumor niches. Fourth, we summarize translational progress, including representative early-phase clinical experiences, manufacturing challenges, and major safety constraints. We also highlight emerging microbiome-disease databases and computational resources that may support target selection, biomarker discovery, and therapy-response stratification. Current evidence supports bacteria as a promising precision modality, particularly for immunologically "cold" or hypoxic tumors; however, major challenges remain in the predictability of intratumoral distribution, host clearance, genetic stability, and long-term safety. Addressing these barriers through rigorous engineering, standardized manufacturing, and clinically meaningful endpoints will be essential for the next generation of bacterial therapeutics in oncology.