<p>Fungi are a vital component of the gastrointestinal microbiota and are increasingly recognized for their critical roles in the initiation, progression, and therapeutic response of digestive tract cancers. Accumulating evidence indicates that specific fungal species contribute to the pathogenesis of various gastrointestinal malignancies—including oral, esophageal, gastric, and colorectal cancers—by promoting chronic inflammation, inducing host DNA damage, and modulating immune responses. Moreover, fungal-bacterial interactions can indirectly influence tumorigenesis by disrupting microbial community homeostasis and altering the functional landscape of the gut microbiome. In this review, we systematically synthesize current evidence from human cohort studies, preclinical models, and multi-omics analyses to delineate mycobiome–cancer associations, elucidate underlying mechanisms, and evaluate emerging diagnostic and therapeutic strategies. Together, these insights position the mycobiome not merely as a bystander but as an active contributor to gastrointestinal carcinogenesis—offering novel opportunities for early detection, risk stratification, and microbiome-targeted interventions in cancer prevention and therapy.</p>