The notion of locally destroying a cancer percutaneously with minimal morbidity and mortality has become accepted as part of the modern armamentarium for treating patients with cancer. Thermal ablation technology has evolved rapidly during the past decades, with substantial technical and procedural improvements that can help to improve clinical outcomes and safety profiles, writes Roberto Iezzi, Rome, Italy.
Radiofrequency ablation has become a touchstone of interventional oncology. The beginnings of what we now know as radiofrequency ablation stretch back to nearly 20 years. The future of ablation will rely on expanding clinical indications, creating the potential for larger areas of ablation, attempting to more accurately control the area of ablation, ensuring the safety of the procedure and looking for greater succesful long-term outcomes in the tumours we ablate. Energy-based ablation includes technologies that destroy a tumour either through thermal (hot or cold) or non-thermal mechanisms.
Radiofrequency ablation is currently the ablation modality supported by the largest number of studies, including randomised controlled trials and meta-analyses. Microwave ablation is gaining acceptance in the medical community and the evidence regarding its benefit in comparison with radiofrequency is increasing, although a recently presented randomised controlled trial has failed to demonstrate its superiority over radiofrequency ablation.
Cryoablation destroys tumoral tissue by freezing, or alternating freezing and thawing. Rapid tissue freezing and thawing produces the greatest cytotoxic effects by disrupting cellular membranes and inducing cell death. Its advantages include the ability to monitor the ice-ball formation during the procedure on imaging and the absence of pain when delivering the treatment.
US-guided high-intensity focused ultrasound (HIFU) treatment for patients with hepatic metastasis offers effective local tumour control with minimal adverse effects whereas MR-guided HIFU for liver lesions is still at an early stage due to the limited therapeutic window caused by the thoracic cage and respiratory motion.
Irreversible electroporation is a new ablative technique that uses high-voltage, low-energy direct current to create nanopores in the cell membrane by the passage of electrons through adjacent cells.
Other emerging technologies are represented by imaging-guiding modalities and assistive techniques for percutaneous treatment. In particular, recent technical advances of imaging fusion have enabled the overlay or side-by-side display of real-time ultrasound images combined with the established fusion of CT/MRI-acquired images during an interventional procedure. Like fusion imaging, contrast-enhanced ultrasound increases RFA performance in terms of localisation and targeting of a tumour. Applying these technique to tumour ablation enhances the identification of target lesions and the feasibility of the intervention.
Recently, the crucial role of multimodal or combination treatment for patients with liver malignancies has been emphasised. In particular, it was demonstrated that combination treatment with transarterial chemoembolization (TACE) and radiofrequency ablation has shown promising clinical results in terms of tumour necrosis and disease-free survival. Combining treatments appears to have superior outcomes compared to those obatined with TACE or radiofrequency ablation alone. These synergistic effects may be due to the decreased blood flow into the target lesions with the additional elimination of adjacent micrometastasis. The recent development of molecular-targeted agents in the treatment for hepatocellular carcinoma has prompted synergies between locoregional tumour ablation and systemic chemotherapy.
To conclude, the true extent of the systemic ramifications of thermal ablation is only now beginning to be appreciated. What is clear is that thermal ablation cannot be considered solely as a locoregional therapy. The resultant inflammatory response, though at present limited and unpredictable, paves the way for an expanded role of thermal ablation as a stimulant to the immune system. Ablation, however, is a double-edged sword and the causes of (and the solutions to) its oncogenic effects need investigation.
Roberto Iezzi is an interventional radiologist, Catholic University, Rome, Italy.