Intratumoral microbiota in the growth of CRC and lung cancer: Comprehensive insights from etiology to therapy.

The tumor microenvironment (TME) contains a diverse intratumoral microbiota (ITM) governing cancer onset, progression, and therapeutic response. This review compares ITM profiles of colorectal and lung cancer, two anatomically distinct malignancies linked via the gut-lung axis, and summarizes microbial detection strategies ranging from cultivation and sequencing to spatial and single-cell technologies. Oral pathobionts such as Fusobacterium nucleatum, Streptococcus, and Veillonella accumulate in both cancers, promoting tumorigenesis through chronic inflammation, immune evasion, genotoxic insults, metabolic reprogramming, and facilitating colorectal cancer lung metastasis via venous drainage and systemic dissemination. Microbial signatures in stool, saliva, blood, and tumor tissue offer non-invasive tools for detection, prognosis, and prediction of immunotherapy resistance, while antibiotics, fecal microbiota transplantation, and engineered live biotherapeutics offer strategies to remodel the TME. This synthesis positions the gut-lung axis as a systemic driver of metastasis and outlines a route toward precision microbiome-based diagnostics and therapeutics.