Three different trade names of microspheres (MS) have been available in Japan since last February. Of those one is for bland embolization and two are exclusively for trans-catheter arterial chemoembolization (TACE). MS have unique characteristics compared to traditional materials. They are spherical, slippery and redistribute themselves after aggregation followed by restoration of the blood flow. As a result of redistribution the embolization effect might be unexpectedly weak. Preparing well agitated and diluted suspension is a clue in minimizing the redistribution as well as mistargeted embolization due to back-flow. In MS-TACE for hepatocellular carcinoma (HCC), 100-300 microns MS is mainly used. At an application of larger MS special attention must be paid to microcatheter compatibility. To optimize the drug absorption to MS an operator should follow the instructions provided by each manufacturer. In the ionic interaction a sodium atom plays a special role. It matters whether the saline or deionized water is used for the chemotherapeutic solution. Both products for MS-TACE are similar in drug eluting profiles. Mistargeted embolization in MS-TACE for HCC includes intestinal ulcer, cholecystitis, pancreatic necrosis and biloma. As uncommon adverse effects pulmonary embolization, posterior reversible encephalopathy syndrome (PRES) and eosinophilic pneumonia are documented.

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Transarterial chemoembolization has been performed for more than 30 years with various improvements introduced since the beginning. Chemoembolization consisting of arterial injection of a mixture of Lipiodol and anticancer drugs followed by the injection of porous gelatin particles using a microcatheter in a selective manner is a mainstay in Japan. By contrast, the use of calibrated microspheres has been prevalent in recent years in chemoembolization or bland embolization of hepatocellular carcinoma worldwide. However, in 2014 the products of calibrated microspheres have been approved in Japan and chemoembolization with drug-eluting microspheres (DC-Beads^® and HapaSphere^®) became one of the choices of treatment. Drug-eluting microspheres are uniform in size and produce sustained release of drug to a tumor. At the current moment, neither chemoembolization with Lipiodol nor with drug-eluting microspheres has surpassed the other. Rather, the search for indications has been promoted in accordance with the characteristics of the respective chemoembolization. Therefore, we have to know the current status of chemoembolization with spherical microspheres. We need to rethink the role of chemotherapeutic agents in chemoembolization through the drug-eluting microspheres and improve the safety and efficacy of it.

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Hepatocellular carcinoma is a particularly common malignancy in Asian countries. In Japan, trans-arterial chemoembolization (TACE) is usually given to patients with intermediate stage hepatocellular carcinoma and conventional transcatheter arterial chemoembolization (cTACE) is the gold standard for the treatment of this stage. cTACE has been performed using lipiodol emulsion mixed with anticancer drugs followed by gelatin sponge particles. After several sessions of cTACE, some patients become refractory to this TACE. From the aspect of world standards, sorafenib is recommended for use in HCC patients who are refractory to TACE with well-preserved liver function. From early 2014, drug eluting beads (DEB) have become commercially available in Japan at last. However use of these new products for HCC treatment has only just begun in Japan. Here, we describe the current status of DEB-TACE for cTACE refractory patients in our limited experience.

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Transcatheter arterial chemoembolization is the world standard therapy for unresectable HCC; however, standard methods are not unified, and several methods including DEB-TACE, B-TACE and cTACE have been used. Embolization concepts are different. Microspheres reach the micro tumor feeder inside or peripheral tumor level and spare the relatively large tumor feeder and do not reach the tumor sinus in DEB-TACE. Iodized oil filled with not only tumor sinus and micro tumor feeder but also peripheral tumor drainage vein and relatively large tumor feeder in B-TACE and cTACE. Tumor response is almost the same between the methods. DEB-TACE has a low rate of post TAE events, especially, abdominal pain, and also has only slight liver enzyme elevation. However, it needs a larger amount of contrast medium and long procedure time compared to B-TACE and cTACE. Elderly or patients who experienced a severe post TAE event are recommended DEB-TACE. Patients with renal insufficiency are recommended B-TACE or cTACE. B-TACE is an easy and effective methods. It exerts a good tumor response when arterio-arterial communication flows favorably. Confirmative angiography with balloon occlusion is necessary before B-TACE. In conclusion, good IVRists need the ability for handling DEB-TACE, B-TACE or cTACE.

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The recent introduction of embolization beads (microspheres) into the Japanese market has generated intense clinical interest. Microspheres are often used for therapeutic purposes of primary hepatocellular carcinoma, and there are still limited opportunities to treat other tumors using microspheres. In this paper, we review the applications of microspheres to various tumors other than primary hepatocellular carcinoma, with a focus on liver metastases and bone tumors.

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