Research on the connection between cancer and the microbiota has become crucial, emphasizing how microbial populations affect the onset, spread, and response to cancer therapy. The microbiota, especially the gut microbiota, is essential for regulating metabolism, inflammatory pathways, and immunological responses which are fundamental to cancer biology. According to studies, some microbial species may have preventive effects while others may encourage the formation of tumors. Through the production of genotoxins and other metabolites, the microbial composition can directly influence carcinogenesis; indirectly, it can influence immune responses and alter the tumor microenvironment. Furthermore, it has been discovered that the microbiota affects the toxicity and effectiveness of cancer treatments such as radiation, chemotherapy, and immunotherapy. A possible therapeutic strategy to enhance the results of cancer treatment is altering the microbiota by nutrition, probiotics, prebiotics, or fecal microbiota transplants. An outline of the complex relationships between cancer and the microbiota is given in this review, highlighting the need for more research to develop microbiome-targeted cancer prevention and treatment options.