Cancer presents a major health concern worldwide. Despite the continuous advances in anticancer therapies, therapeutic failure is still evident due to resistance to anticancer drugs and their adverse side effects. A growing body of evidence illustrates a bidirectional interaction between the gut microbiota composition and the success of anticancer therapies. The gut microbiome can influence the host response to chemo- and immunotherapeutic drugs either by modulating the efficacy or toxicity. In particular, the gut microbiota can regulate the efficacy of immune checkpoint inhibitor therapy by modulating the activation of immune responses to cancer. Moreover, intratumor bacteria have been found to exhibit wide-ranging effects on cancer biology. At the same time, anticancer treatments themselves can significantly alter the gut microbiota composition, leading to disruption of homeostasis and dysbiosis, contributing to the severity of side effects.

To date, there are various tools including the emerging computational metagenomic, metabolomic, and gnotobiotic models that allow researchers to learn about the underlying molecular pathways implicated in drug-microbiome interactions. Given that most studies investigating how microbiota modulate cancer therapy have been carried out in animal models, translation of these preclinical findings to the clinic still poses a significant challenge. Exploring the distinctive microbial signatures associated with the cancer types and stages may be used as a biomarker, a diagnostic tool, or a therapeutic target. Considering these observations, therapeutic interventions targeting the gut microbiota could be one of the next frontiers for precise and personalized therapies for cancer.

This Special Issue aims to cover recent advances and novel research trends regarding the role of the gut microbiome in cancer treatment. Authors are welcome to submit original research and review articles covering, but not limited to, the impact of the gut microbiome on the pharmacology of chemotherapeutics or immunotherapeutics, the molecular events behind the microbiome-anticancer drug interactions, or the experimental and computational approaches that bridge the gap between basic and clinical microbiome research related to anticancer drugs. In addition, studies investigating microbial population structure and function in relation to the development of cancer, tumor stage, prognosis, and response to therapy, as well as the potential of microbial-targeted therapy to improve anticancer drug safety and efficacy, are welcome.

Potential topics include but are not limited to the following:

• Impact of gut microbiome on the pharmacology of chemotherapeutics or immunotherapeutics
• Analysis of specific pathobionts, their oncogenic potential, and underlying mechanisms
• Investigations of microbial population structure and function in relation to the development of cancer, tumor stage, prognosis, and response to therapy
• Experimental and computational approaches that bridge the gap between basic and clinical microbiome research related to anticancer drugs
• Model systems in the study of microbiome-anticancer drug interactions
• Potential of microbial-targeted therapy to improve anticancer drug safety and efficacy