Transarterial chemoembolization using iodized oil for unresectable hepatocellular carcinoma: perspective from multistep hepatocarcinogenesis

Transarterial chemoembolization (TACE) using iodized oil (Lipiodol(®)) (Lp-TACE) as a carrier of chemotherapeutic agents has been routinely performed to control hepatocellular carcinomas (HCC) in Japan, and its use has yielded fairly beneficial therapeutic results. Lipiodol is thought to pass through the tumor sinusoids of HCC and reach the outflow drainage areas, namely, the portal venous side of the tumor. By doing this, Lipiodol blocks not only the tumor's arterial inflow but also its portal venous outflow, providing sufficient ischemic effects. It is known that the inflow blood system, tumor sinusoids, and outflow blood system change drastically during the process of multistep hepatocarcinogenesis; thus, it is reasonable to postulate that the distribution of Lipiodol and the subsequent therapeutic effect of Lp-TACE may also change during that process. Arterial inflow to HCC is highest for moderately differentiated HCC (mHCC) and is relatively low in well or poorly differentiated HCC (wHCC and pHCC, respectively). It has been suggested that the metabolic state of wHCC and mHCC is aerobic, while that of pHCC is anaerobic. The tumor sinusoids in wHCC and mHCC are small in size and large in number, while those in pHCC are large in size and small in number. This finding results in a greater chance of tumor cell exposure to chemotherapeutic agents in the former and a lesser chance in the latter. The outflow tract, namely, the drainage system via the residual portal venous branches within the pseudocapsule, is more complete in mHCC and pHCC and less so in wHCC. Considering all of these components of HCC of different histological grades, Lp-TACE should have the greatest effect on mHCC and a relatively low effect on wHCC and pHCC. To achieve consistently high therapeutic results, it is important to consider these components, which affect the sensitivity of HCC to Lp-TACE, to maximize both the chemotherapeutic and ischemic effects of this therapy.