Fungi inhabit various sites in the human body and have been increasingly linked to tumorigenesis. Recent advances in omics technologies have revealed that specific fungi are enriched in tumor tissues, suggesting a role in cancer development. Fungi influence tumorigenesis through factors such as host immunity, bioactive metabolites, and interactions with the bacterial microbiome. The presence of fungi in tumor tissues varies by cancer type, with some species like Candida and Malassezia associated with specific cancers. Fungi can transition from commensal to pathogenic, contributing to tumor progression. Intratumoral fungi may serve as diagnostic and therapeutic targets, as they are influenced by factors such as diet, fecal microbiota transplantation, and probiotics. Studies have shown that fungi can modulate immune responses, promote inflammation, and affect tumor cell metabolism. For example, Candida species can increase the accumulation of myeloid-derived suppressor cells (MDSCs), which promote tumor growth. Fungal metabolites and toxins can induce genetic and epigenetic changes, contributing to cancer. Biofilms and fungal extracellular vesicles also play roles in tumor progression. The interaction between fungi and the microbiome, as well as host factors, influences fungal enrichment and carcinogenicity. Research highlights the potential of intratumoral fungi in cancer diagnosis and treatment, though many questions remain about their exact mechanisms and roles. Future studies aim to clarify the factors determining fungal abundance in tumors, their origins, and their interactions with the immune system. Understanding these aspects could lead to new therapeutic strategies for cancer.Fungi inhabit various sites in the human body and have been increasingly linked to tumorigenesis. Recent advances in omics technologies have revealed that specific fungi are enriched in tumor tissues, suggesting a role in cancer development. Fungi influence tumorigenesis through factors such as host immunity, bioactive metabolites, and interactions with the bacterial microbiome. The presence of fungi in tumor tissues varies by cancer type, with some species like Candida and Malassezia associated with specific cancers. Fungi can transition from commensal to pathogenic, contributing to tumor progression. Intratumoral fungi may serve as diagnostic and therapeutic targets, as they are influenced by factors such as diet, fecal microbiota transplantation, and probiotics. Studies have shown that fungi can modulate immune responses, promote inflammation, and affect tumor cell metabolism. For example, Candida species can increase the accumulation of myeloid-derived suppressor cells (MDSCs), which promote tumor growth. Fungal metabolites and toxins can induce genetic and epigenetic changes, contributing to cancer. Biofilms and fungal extracellular vesicles also play roles in tumor progression. The interaction between fungi and the microbiome, as well as host factors, influences fungal enrichment and carcinogenicity. Research highlights the potential of intratumoral fungi in cancer diagnosis and treatment, though many questions remain about their exact mechanisms and roles. Future studies aim to clarify the factors determining fungal abundance in tumors, their origins, and their interactions with the immune system. Understanding these aspects could lead to new therapeutic strategies for cancer.