Managing locally advanced rectal cancer continues to pose complex clinical challenges for multidisciplinary care teams. Standard neoadjuvant chemoradiotherapy produces a complete pathological response in only a modest fraction of treated individuals. Consequently, surgical oncologists actively explore innovative interventions to enhance local tumor downstaging and improve sphincter preservation rates. Emerging clinical evidence highlights the utility of chemoembolization in rectal cancer as an effective locoregional drug delivery strategy. By delivering concentrated cytotoxic agents directly into tumor-feeding vessels, endovascular therapy achieves high intratumoral concentrations while sparing healthy tissues from systemic toxicity. This updated systematic review provides crucial insights into how transarterial approaches are reshaping locally advanced rectal cancer management.

The Biological Rationale for Chemoembolization in Rectal Cancer

Standard neoadjuvant chemoradiotherapy often leaves viable residual disease in the rectal wall and regional mesorectal lymph nodes. Furthermore, standard systemic chemotherapy distributes cytotoxic agents non-selectively throughout the circulation, frequently causing debilitating toxicities such as myelosuppression and severe peripheral neuropathy. Therefore, interventional radiologists and surgical oncologists developed transcatheter rectal arterial chemoembolization to overcome these biological hurdles. The primary rationale relies on superselective microcatheterization of the superior rectal artery and its direct feeding branches. Consequently, interventionalists deliver concentrated antineoplastic agents directly into the tumor microenvironment. At the same time, microparticles or lipid emulsions mechanically occlude tumor neovasculature, inducing profound local ischemia and tissue hypoxia. In addition, ischemic stress amplifies vascular permeability and retards cytotoxic drug washout from the tumor bed. This targeted therapeutic approach maximizes cellular necrosis within the rectal mass while minimizing systemic drug exposure. In addition, this localized delivery mitigates systemic toxicities that frequently derail curative treatment courses. Moreover, extensive ischemic necrosis stimulates the release of tumor neoantigens that may prime host anti-tumor immune responses. Hence, endovascular chemoembolization offers an attractive locoregional complement to standard multimodal neoadjuvant therapy protocols.

Systematic Review Evidence and Pathological Response Outcomes

The updated systematic review synthesized clinical outcomes across nine published studies comprising 822 patients with locally advanced rectal cancer. Among these individuals, 582 patients received transarterial chemoembolization or transcatheter rectal arterial chemoembolization. Notably, researchers conducted the vast majority of these clinical investigations across tertiary academic medical centers in China. Across all evaluated cohorts, investigators reported pathological complete response rates ranging from 10% to 44.74%. Furthermore, comparative studies demonstrated that adding transcatheter rectal arterial chemoembolization with oxaliplatin to standard chemoradiotherapy significantly reduced poor histological responses. Specifically, patients in the chemoembolization cohorts showed markedly lower rates of tumor regression grade 3. In the largest comparative cohort of 236 patients, only 16.18% of embolized patients exhibited tumor regression grade 3 compared to 35% in control cohorts. Additionally, exploratory subgroup analyses demonstrated a tangible survival benefit in patients who exhibited tumor regression grade 3. This finding suggests that arterial intervention may salvage outcomes in chemoradiotherapy-resistant disease, confirming the remarkable downstaging power of targeted endovascular delivery.

Breakthroughs in Chemo-Immunoembolization and the CIETAI Protocol

Immune checkpoint inhibitors have revolutionized modern oncology, yet their single-agent efficacy remains disappointing in mismatch repair-proficient rectal cancer. Moreover, intravenous delivery of immune checkpoint inhibitors carries persistent risks of severe, debilitating immune-related adverse events. To overcome these immunologic barriers, clinical investigators designed the first-in-human chemo-immunoembolization with transcatheter rectal arterial intervention protocol. Specifically, this phase II trial evaluated sequential intra-arterial infusion of oxaliplatin and the anti-PD-1 monoclonal antibody tislelizumab. Following this locoregional delivery, patients completed concurrent chemoradiotherapy and subsequent radical surgery. Remarkably, this innovative approach produced the highest pathological complete response rate in the systematic review at 44.74%. Furthermore, the major pathologic response rate reached 65.79%, while the anal preservation rate attained 84.21%. Notably, clinicians recorded zero grade 3 or 4 immune-related adverse events throughout the trial. Consequently, direct intra-arterial delivery of immunotherapy safely primes the local immune microenvironment. In addition, synergistic vascular occlusion and checkpoint blockade effectively break local immune tolerance without causing systemic autoimmune toxicity.

Procedural Safety, Complication Profiles, and Surgical Feasibility

Delivering endovascular embolization into hollow pelvic viscera historically raised theoretical concerns regarding ischemic bowel perforation and intractable strictures. However, recent systematic data demonstrate that transcatheter rectal arterial chemoembolization maintains a favorable, predictable safety profile. Overall, interventional radiologists recorded very few major procedural complications across the published clinical series. Most patients experienced only transient, mild post-embolization symptoms, including low-grade pyrexia, self-limiting tenesmus, and dull pelvic discomfort. Furthermore, surgical oncologists reported that preoperative endovascular embolization did not compromise subsequent total mesorectal excision. In addition, rates of anastomotic leakage, intraoperative hemorrhage, and postoperative wound complications remained comparable to conventional chemoradiotherapy cohorts. Precise superselective microcatheter navigation preserves critical pelvic collateral blood flow, thereby preventing transmural ischemic necrosis of the rectal wall. Furthermore, meticulous angiographic evaluation of pelvic arterial anatomy prevents accidental non-target embolization of adjacent pelvic viscera. Thus, careful preoperative vascular imaging and meticulous microcatheter technique reliably ensure patient safety. Consequently, surgical teams can proceed confidently to definitive radical resection or organ-preserving approaches.

Multidisciplinary Implications and Future Clinical Trial Horizons

The compelling findings of this systematic review introduce valuable therapeutic opportunities for multidisciplinary colorectal cancer teams. Currently, standard total neoadjuvant therapy protocols frequently cause cumulative systemic toxicities that force premature dose reductions or treatment cessations. Therefore, incorporating locoregional transarterial chemoembolization could optimize local tumor regression while maintaining systemic functional status. In particular, this targeted approach offers tremendous promise for low-lying rectal lesions where achieving maximum downsizing dictates sphincter preservation. Moreover, the remarkable response observed in mismatch repair-proficient tumors suggests that intra-arterial immunotherapy can convert immunologically cold tumors into responsive lesions. Nevertheless, clinicians must interpret these promising results within their methodological context. Most available studies remain retrospective, non-randomized, and geographically centered in East Asia. Consequently, the international oncology community urgently requires large prospective randomized controlled trials to confirm long-term survival advantages. Additionally, multidisciplinary tumor boards must follow these emerging trials closely when considering organ preservation strategies. As clinical research advances, standardized microcatheter protocols and calibrated embolic delivery will solidify the clinical role of endovascular interventions in rectal cancer care.

What is transcatheter rectal arterial chemoembolization in rectal cancer?

Transcatheter rectal arterial chemoembolization is an image-guided endovascular intervention designed for locally advanced rectal cancer. An interventional radiologist navigates a microcatheter superselectively into rectal tumor-feeding arteries. The specialist then infuses concentrated chemotherapeutic agents, such as oxaliplatin, followed by embolic particles. Consequently, this targeted delivery achieves high intratumoral cytotoxic concentrations, restricts vascular supply, and minimizes systemic exposure, thereby enhancing pathological downstaging prior to surgery.

How does intra-arterial chemo-immunoembolization improve immunotherapy response?

Historically, mismatch repair-proficient rectal cancers show limited sensitivity to standard intravenous immune checkpoint inhibitors. In contrast, chemo-immunoembolization directly infuses agents like tislelizumab and oxaliplatin into rectal feeding arteries. This targeted approach induces localized tumor ischemia, cellular necrosis, and antigen release while depositing high antibody concentrations locally. Consequently, it ignites a potent anti-tumor immune response within the tumor microenvironment without precipitating severe systemic immune-related toxicities.

Does preoperative transarterial chemoembolization increase surgical complications?

Clinical evidence demonstrates that preoperative transarterial chemoembolization does not significantly increase surgical morbidity. Superselective catheterization preserves vital pelvic collateral circulation, thereby preventing extensive bowel wall necrosis or pelvic floor ischemia. Consequently, patients who undergo total mesorectal excision following chemoembolization exhibit anastomotic leakage and wound complication rates comparable to those receiving standard neoadjuvant chemoradiotherapy, confirming that endovascular preparation is surgically safe and feasible.

Disclaimer: This content is for informational and educational purposes only and is not intended to serve as medical advice, diagnosis, or treatment. Medical knowledge and clinical guidelines evolve continuously. Healthcare professionals should exercise their independent clinical judgement when making treatment decisions. Refer to the latest local and national guidelines for clinical practice.

References

1. Saadeh OA et al. Transarterial Chemoembolization and Chemo-Immunoembolization in Locally Advanced Rectal Cancer: An Updated Systematic Review. Asia Pac J Clin Oncol. 2026 Nov 12. doi: 10.1111/ajco.70225. PMID: 43016369.
2. Yang W, Li C, Luo J, et al. Transcatheter rectal arterial chemoembolization with oxaliplatin and concurrent chemoradiotherapy in patients with locally advanced rectal cancer: A retrospective comparative study. Eur J Surg Oncol. 2025;51(5):109582.
3. Yang W, Wang J, Gan J, et al. First in human intraarterial delivery of tislelizumab for the treatment of pMMR locally advanced rectal cancer: A single-arm, open label, phase II clinical trial. Transl Oncol. 2024;50:102154.