Systematic Review of Monocyte Transcriptomic Profiles as Diagnostic and Prognostic Biomarkers in Colorectal Cancer

Colorectal cancer (CRC) remains a major global health burden and a leading cause of cancer-related morbidity and mortality. Current blood-based biomarkers lack sufficient sensitivity and specificity, particularly for early detection. In this context, circulating immune-cell transcriptomic profiling has emerged as a promising minimally invasive approach. This systematic review was conducted following a PROSPERO-registered protocol (CRD42024604757) and PRISMA 2020 guidelines to evaluate the diagnostic and prognostic potential of circulating monocyte-related transcriptomic profiles in CRC. Of 295 records identified, six studies met the inclusion criteria. The available evidence consistently supports the diagnostic value of circulating transcriptomic profiles in distinguishing patients with CRC from healthy individuals and in reflecting tumour-associated immune alterations. Monocyte-related signatures, including CXCR2⁺ monocytes, were associated with disease stage and metastatic features. Epitranscriptomic modifications, such as m6A and m5C, further reinforced their diagnostic relevance, with some studies reporting higher diagnostic accuracy than classical biomarkers. In contrast, evidence for prognostic value remains limited, heterogeneous, and often indirect, largely due to small sample sizes, methodological variability, and reliance on public datasets. Overall, circulating immune-cell transcriptomic profiles are promising non-invasive biomarkers for CRC detection and characterization, although their prognostic utility remains unclear. Methodological heterogeneity limits clinical applicability, highlighting the need for standardized, CRC-specific studies with cell-type-resolved approaches.