Interventional Oncology: A field on the move

The future of the fledgling field known as interventional oncology lies in the development of multi-modal combination therapies and fusion imaging, predicted at the annual meeting of the Cardiovascular and Radiological Interven-tional Society of Europe. Inter-ventional oncology is the term coined for minimally invasive, non-surgical destructive procedures performed on primary tumors and metastases under real-time imaging guidance, with curative  intent or for palliation. When we discussed naming this new branch of medicine, we decided to call it interventional oncology, even though the correct name should have been ‘image-guided interventional oncology.’ That’s too long. But the imaging is crucial. The rapidly growing field reached several milestones during the past two years.

Earlier this year, the first World Congress on Interventional Oncology was held. And last year, for the first time, the Radiological Society of North America featured an interventional oncology track each day throughout its annual meeting. Today, the most frequently performed interventional oncology procedure is percutaneous radio frequency ablation (RFA) of tumors in a wide variety of organs, with the liver leading the way. Industry watchers project continued exponential annual growth worldwide in the number of RFA procedures performed. But RFA has its limitations. Its efficacy in completely destroying large tumors drops off sharply, and cancers located adjacent to critical organ structures are problematic.

 For these reasons, other ablative technologies are being developed, including cryoablation, laser hyperthermia, and microwave ablation. Each has its strengths and shortcomings. Particularly promising, is high-intensity focused ultrasound (HIFU). Its advantage lies in extremely precise targeting; the HIFU beam can pass harmlessly through nearby critical structure while focusing on the tumor. At present, HIFU sessions are impractically long, but that will change with further technical advances.

The next few years will bring a variety of creative combination of RFA  plus transarterial chemo-embolization with doxorubicin, cisplatin, or other chemotherapy agents has been shown to be more effective than RFA alone, enabling interventionalists to address larger, more complex tumors. Promising results have also been reported for RFA coupled with temporary venous occlusion.

Novel methods of targeted chemotherapeutic drug release are being developed. Intravenously administered liposomal doxorubin and RFA have shown a synergistic effect, the immediate tumor destruction is due to RFA, but weeks later there is further destruction due to the doxorubicin.  Chemotherapeutic agents are also being hitched to thermosensitive liposomes that open only when struck by RFA or, more likely in the future, by HIFU. The result is release of the drug precisely where it will have the maximum local effect and minimal systemic toxicity.

CT and MRI are the imaging modalities best suited for interventional oncology procedural planning and follow-up, while ultrasound is the simplest and least expensive imaging method for real-time guidance and monitoring of tumor ablation. But ultrasound can’t adequately visualize all tumors. Imaging systems that combine real-time ultrasound with CT or MRI images offer the best solution. A few such systems are now commercially available, with more to come. They permit the images to be overlapped or displayed side by side. Other promising imaging developments include 3-D rotational angiography for transarterial chemoembolization and PET to differentiate cancer from inflammation.