Enhancing Targeted Colorectal Cancer Therapies with Natural Products: Mechanistic Pathways

Background: Colorectal cancer (CRC) remains a leading cause of mortality worldwide, with a significant proportion of patients presenting with metastatic disease (mCRC). While molecularly targeted therapies, including anti-EGFR and anti-VEGF agents, have improved survival outcomes, their efficacy is often limited by drug resistance, toxicity, and high costs. There is a growing need for sustainable strategies to enhance therapeutic efficacy. Methods: This review explores the emerging role of plant-derived compounds as synergistic adjuvants. Specifically, PubMed, Scopus, and Web of Science were searched for English-language articles published between January 2004 and June 2026, using combination of terms related to colorectal cancer, metastatic disease, anti-EGFR/anti-VEGF targeted therapy, phytochemicals/natural products, and gut microbiota; both primary studies and reviews were eligible. Results: Targeted therapies such as cetuximab and bevacizumab are the standard of care but face challenges related to RAS/BRAF mutations and primary tumour location. Clinical data demonstrate that while cetuximab improves overall survival in patients with RAS wild-type, left-sided tumours (median OS 31 vs. 26 months; HR 0.76, p = 0.012), progression-free survival remains comparable to that of bevacizumab. Concurrently, natural products like Vitis vinifera, Dendrobium candidum, and quercetin demonstrate significant preclinical potential in inhibiting angiogenesis, inducing apoptosis, and modulating the tumour microenvironment. The gut microbiome, particularly Fusobacterium nucleatum (whose reported prevalence varies widely across cohorts and reaches up to ~98% of CRC tissues only in selected series), has emerged as a key factor in chemoresistance. It should be emphasised that the great majority of the phytochemical-targeted therapy combinations discussed here are currently supported primarily by preclinical (in vitro and animal) studies rather than by clinical trials. Conclusions: Integrating evidence-based phytochemicals with conventional targeted therapies is a mechanistically compelling and potentially sustainable strategy that may enhance therapeutic efficacy, help overcome resistance, and mitigate adverse effects in mCRC management. However, because current support is largely preclinical, these combinations should be regarded as hypothesis-generating and require validation in prospective, biomarker-stratified clinical trials before clinical adoption.