BACKGROUND: Colorectal cancer (CRC) presents a complex tumor microenvironment influenced by genetic and microbial factors. Microbial DNA from the gut and tumor microenvironment can translocate into the bloodstream, forming a circulating microbiome associated with prognosis and clinicopathological features. This study investigates the peripheral venous blood microbiome in CRC patients using 2bRAD-M sequencing and evaluates its clinical significance. METHODS: Peripheral venous blood samples from 29 CRC patients (19 males, 10 females
mean age 57 years) and 10 healthy controls were analyzed to assess microbial diversity. Additionally, 20 tumor tissue samples from CRC patients were examined via RT-qPCR to validate blood-tumor microbial correlations. Statistical analyses evaluated associations between microbial abundance and clinical features, including metastasis and PD-L1 Combined Positive Score (CPS). Comparative analyses between CRC patients and healthy controls were performed to identify disease-specific microbial signatures. RESULTS: A total of 270 microbial species were identified, with dominant phyla including Actinomycetota, Bacillota, Bacteroidota, and Pseudomonadota. Bosea lupini was significantly associated with metastasis stage (p = 0.034), while Mycobacterium tuberculosis (p = 0.022), Porphyromonas pasteri (p = 0.017), and Bosea lupini (p = 0.045) correlated with CPS. Microbes such as Bosea lupini, Ralstonia mannitolilytica, and Porphyromonas pasteri suggested potential tumor-derived translocation into the bloodstream. CONCLUSION: This study identifies a distinct peripheral venous blood microbiome in CRC patients, highlighting specific microbes associated with clinicopathological features and disease progression. These findings suggest the potential of blood microbiomes as noninvasive biomarkers for CRC prognosis and therapeutic targets, warranting further investigation in larger cohorts.