Letter: is microwave ablation superior to radiofrequency ablation for early stage hepatocellular carcinoma? Authors' reply

EDITORS,

We thank Ge et  al for their interest in our work.1 They conducted a pooled analysis to compare microwave ablation (MWA) and radiofrequency ablation (RFA) for early stage hepatocellular carcinoma (HCC), and found that both treatments provided similar oncological outcomes.2 Thus, they concluded that MWA might not be superior to RFA in a real world setting. However, there were many heterogeneities and several shortcomings among those studies included in the pooled analysis, making it hard to directly compare their conclusion to ours.1 In the study of Ding et  al,3 they admitted that the MWA group had more tumours >3 cm (26.7%) than the RFA group (15.3%), which would compromise the treatment efficacy of MWA. Similarly, Santambrogio et  al4 preferred to use MWA in treating HCC >2 cm, and to use RFA for smaller lesions (2.1 cm vs 1.9 cm, P = 0.008) which could also impair the treatment efficacy of MWA. Even so, the local tumour progression rate was still higher in the RFA group than in the MWA group (21.2% vs 8.3%, P = 0.034). Regarding the randomised controlled trial (RCT) conducted by Yu et  al,5 they found that MWA showed better tumour inactivation ability than RFA for tumours of 3.0-5.0 cm (6.7% vs 13.0%) and tumours adjacent to vessels (4.3% vs 7.7%), which implied better prospects for MWA due to its higher thermal efficiency and insensitivity to the heat-sink effect. The RCT conducted by Abdelaziz et  al,6 could have been limited by its short follow up (approximate 40 months) and a high rate of patients lost to follow-up (52.2%). However, compared with RFA, the study still demonstrated an increased 2-year overall survival in the MWA group although without a statistically significant difference (62% vs 47.4%, P = 0.49) and a significantly lower incidence of local recurrence (3.9% vs 13.5%, P = 0.04). The design of the RCT conducted by Vietti Violi et  al7 to compare MWA and RFA in treating HCC up to three lesions of 4 cm or less was good. However, the lesion size in the study of Vietti Violi et  al was smaller than that in our study (1.8 cm vs 2.3 cm) due to different inclusion criteria. Hence, our study found that MWA was superior to RFA when larger tumours inside the Milan criteria were included, as indicated by a systematic review that MWA had potential benefit to treat larger lesions.8

Although it is meaningful to perform such a pooled analysis, our study applied propensity score matching to balance the baseline characteristics between MWA and RFA, and found that RFA had comparable efficacy to MWA for solitary HCC ≤3 cm, but was inferior to MWA for treating HCC within the Milan criteria. Finally, selection bias might not have been completely avoided due to the retrospective nature of our study. Therefore, more well-designed, multicentre RCTs are needed to determine which ablation modality is superior. More importantly, more advanced ablation apparatus and modalities should be developed to offer better medical care for patients with HCC.