Tehran University of Medical Sciences Basic & Clinical Cancer Research 2228-6527 16 4 2025 11 08 216 229 Maryam Abbaspour Cancer Biology Research Center, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran Marveh Rahmati Cancer Biology Research Center, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran Mahdi Aghili Radiation Oncology Research Center -Cancer Institute, Tehran University of Medical Sciences Mahdiheh Salehi Cancer Biology Research Center, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran Saman Asadi Cancer Biology Research Center, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran Yasaman Saburi Department of Microbiology, Faculty of Advanced Sciences and Technology, Tehran Medical Sciences Branch, Islamic Azad University, Tehran, Iran Saba Zeighami Department of Microbiology, Faculty of Advanced Sciences and Technology, Tehran Medical Sciences Branch, Islamic Azad University, Tehran, Iran Zahara Allahyar Vali-E-Asr Reproductive Health Research Center, Family Health Research Institute, Tehran University of Medical Sciences. Saeid Amanpour Cancer Biology Research Center, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran 2025 08 03 2025 09 14 Breakthroughs in sequencing technologies have overturned the notion that tumor tissues are sterile, revealing that a wide array of bacteria, fungi, and viruses—collectively known as the intratumoral microbiota—inhabit tumors across diverse cancer types. These microorganisms, which can colonize tumors via mucosal barrier disruption, adjacent tissue spread, or hematogenous routes, have emerged as critical modulators of the tumor microenvironment. Mechanistic studies demonstrate that intratumoural microbiota influence cancer biology by inducing genomic instability, altering epigenetic landscapes, promoting chronic inflammation, evading immune surveillance, and reshaping tumor metabolism. The diversity and composition of these microbial communities vary by tumor type and stage, with distinct microbial signatures linked to patient prognosis and therapeutic response. As research progresses, the intratumoural microbiota are being recognized not only as biomarkers for early cancer detection and prognosis but also as promising targets for innovative therapies, particularly in the context of immunotherapy. While challenges remain in elucidating the origins, functions, and safe manipulation of these microbes, ongoing advances hold the potential to revolutionize cancer diagnosis, prognosis, and treatment through microbiota-targeted strategies. This review summarizes the characteristics and origins of intratumoural microbiota, their prognostic significance, and their emerging applications in cancer therapy. https://bccr.tums.ac.ir/index.php/bccrj/article/view/580