Insufficient radiofrequency ablation therapy may induce further malignant transformation of hepatocellular carcinoma

Background Radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC) is a thermoablative technique to kill tumor tissue by generating areas of coagulative necrosis. Recent reports have raised concern that RFA may lead to a local recurrence of HCC with an aggressive phenotype and unfavorable prognosis, suggesting that RFA may induce further malignant transformation of HCC. However, the biological effects of RFA on HCC cells have not been directly analyzed. The aim of this study was to determine whether heat stress of the type associated with RFA induces malignant transformation of HCC. Methods We assessed the sensitivity of three HCC cell lines (HepG2, Alexander, and Huh7) to heat treatment for 10 min. We then determined the temperature at which a heat-resistant subline can be generated. We established and expanded sublines that survived heat treatment. And their proliferation rates, heat sensitivities, and invasive capacities were further examined. Results All HepG2 died after 48°C treatment, whereas 49°C treatment was required to kill all Alexander and HuH7. We generated 20 sublines for each parental cell line. A HepG2 subline, HepG2#18, proliferated 100% faster than parental HepG2. Moreover, HepG2#18 survived after 50°C treatment, whereas all parental HepG2 died after heat treatments at 48°C or higher. Conclusion Our results showed that even a single heat treatment could induce further transformation of an HCC cell line. Our results suggest that an insufficient treatment of HCC by RFA that enables survival of some cells might induce further malignant transformation in vivo.