Pitfalls in the radiological and pathological correlation of tumour response rates of hepatocellular carcinoma following radiofrequency ablation

According to the American Association for the Study of Liver Diseases (AASLD) guidelines, radiofrequency ablation (RFA) is a safe and effective treatment for patients with unresectable hepatocellular carcinoma (HCC). In most studies, the initial complete tumour response rates of small HCCs <= 3 cm following RFA have been reported as more than 90% or 95%, and local tumour progression rates have been reported as approximately 10% or 20%. Notwithstanding these promising clinical outcomes, the complete tumour response rates for HCC following RFA as determined by conventional histopathological diagnostic criteria have been reported to be less than 50% in many recent reports. While considering that most cases of local tumour progression of HCC are known to occur within two years following RFA, it may not be reasonable to assume that clinical and radiological examinations have significantly overestimated the tumour response rates. On the contrary, it is likely that the conventional histopathological examination techniques may have underestimated the tumour response rates. The apparent discrepancy between the histopathological and the radiological tumour response of radiofrequency ablation for hepatocellular carcinomas can be attributed to several histological features, such as thermal fixation or apoptosis, that were not included in the conventional histopathological diagnostic criteria. However, a robust conclusion cannot be derived because of lack of adequate controlled studies, and further well designed prospective multicentre trials will be helpful to solve this issue.