Traditionally, the role of the gut microbiome has been evaluated in relation to diseases and pathologies affecting the gut. However, recent clinical trials have highlighted the significant impact of the microbiome on extraintestinal diseases. Similarly, studies have transitioned from exploring the impacts of the microbiome and the efficacy of methods like fecal microbiota transplantation (FMT) on intestinal diseases to actively modulating the microbiome to influence non-intestinal conditions. Therefore, it is not far-fetched that in this chapter we will examine the impact of the microbiome on the second cause of death, cancer, and in this way put the most important and most up-to-date microbiome modification technique, FMT, under the microscope. Therefore, we will address questions such as how this technique affects the tumor microenvironment (TME), the current position of microbiome elements on cancer, and how to manipulate the gut microbiome to enhance therapeutic responses for different cancer types. In addition, we also collect recent clinical trials and relevant information and discuss safety and side effects to provide a foundation for the development of personalized medicine in further studies.