The occurrence of microorganisms has been confirmed in the tumor microenvironment (TME) of many different organs. Microorganisms (e.g., phage, virus, bacteria, fungi, and protozoa) present in TME modulate TME to inhibit or promote tumor growth in species-dependent manners due to the special physiological and pathological features of each microorganism. Such microorganism-TME interactions have recently been emulated to turn microorganisms into powerful cancer theranostic agents. To facilitate scientists to explore microorganisms-TME interactions further to develop improved cancer theranostics, here we critically review the characteristics of different microorganisms that can be found in TME, their interactions with TME, and their current applications in cancer diagnosis and therapy. Clinical trials of using microorganisms for cancer theranostics are also summarized and discussed. Moreover, the emerging technology of whole-metagenome sequencing that can be employed to precisely determine microbiota spectra is described. Such technology enables scientists to gain an in-depth understanding of the species and distributions of microorganisms in TME. Therefore, scientists now have new tools to identify microorganisms (either naturally present in or introduced into TME) that can be used as effective probes, monitors, vaccines, or drugs for potentially advancing cancer theranostics to clinical applications.

RGD-displaying phage, fibrin, and neural stem cells (NSCs) are integrated to form a fiber-like hydrogel, which promotes preferential differentiation of NSCs and serves as a nerve graft to repair the long-gap nerve defect by enhanced neurogenesis.