The human microbiome plays a pivotal role in immune modulation, and its influence on the development and progression of cancer has gained increasing recognition. Based on the concept of cancer immunotherapy, personalized approaches are extensively explored to address the limitations and challenges associated with achieving optimal treatment outcomes. This review examines the emerging field of customized probiotics and their profound impact on tailoring cancer immunotherapies. It provides an overview of cancer immunotherapies, the intricate relationship between the microbiome and cancer, and the concept of dysbiosis in disease progression. By delving into the mechanisms through which probiotics modulate the microbiome, this review highlights the evidence supporting their potential application in treating cancer patients. The review also emphasizes the rationale behind personalized probiotics in cancer treatment, discussing strategies for tailoring probiotics to individual patients with case studies demonstrating their efficacy. In addition, it explores the underlying synergistic mechanisms between probiotics and immunotherapies, focusing on their effects on the tumor microenvironment and immune cell activity. Challenges and ethical considerations are addressed, including the potential risks associated with personalized probiotics, and future directions for research and clinical applications are proposed. Finally, the clinical implications and translational potential of integrating personalized probiotics into cancer treatment protocols are examined, emphasizing the need for standardized approaches and regulatory considerations. This review aims to provide a comprehensive understanding of the role of personalized probiotics in shaping the landscape of cancer immunotherapies, paving the way for innovative and tailored therapeutic interventions.