Emerging Perspectives on How Metallic Nanoparticles and Their Oxide Forms Interact with the Tumor Microenvironment

Cancer remains one of the most formidable health challenges worldwide. Extensive research has shown that tumor progression is not driven solely by malignant cells but is profoundly shaped by the tumor microenvironment (TME), which influences cancer initiation, immune evasion, and metastatic spread. Consequently, the TME has become an increasingly compelling therapeutic target. Nanotechnology has transformed cancer diagnostics and therapy, with metallic nanoparticles (mNPs) gaining particular attention due to their distinctive physicochemical properties and broad therapeutic potential. However, their interactions within the TME remain insufficiently understood, particularly with the non-cancerous cellular components, such as Cancer-Associated Fibroblasts (CAFs), Tumor-Associated Macrophages (TAMs), Dendritic Cells (DCs), Natural Killer (NK) cells, and T cells. Most existing reviews emphasize nanoparticle interactions with non-cellular TME components, such as the extracellular matrix, while far less attention has been given to their effects on cellular constituents (a gap this work specifically addresses). Although several molecular pathways through which mNPs modulate TME-resident cells have been identified, these likely represent only a small portion of the underlying mechanisms explored in this review. Progress in the field is further hindered by the limited availability of physiologically relevant experimental models; current in vitro and in vivo systems often fail to capture the complexity and dynamic heterogeneity of the TME. These limitations highlight the urgent need for more comprehensive and mechanistically grounded studies to validate the TME as a viable therapeutic target for nanoparticle-based cancer interventions. In particular, deeper insights into how mNPs influence immune regulation, stromal remodeling, and metabolic reprogramming within the TME will be essential for unlocking their full therapeutic potential in oncology.