Are modified RECIST the gold standard for response assessment of lung tumours treated with microwave ablation?

Abstract

Introduction: mRECIST were introduced in early 2000 for radiofrequency ablation (RFA) of lung tumours. This retrospective study was performed to evaluate mRECIST in the assessment of lung tumours treated with microwave ablation (MWA). Material and Methods: All percutaneous CT–guided MWA of lung tumours performed between June 2010 and December 2016 were identified and cases with at least 10 months follow-up were included. The therapeutic response was evaluated based on mRECIST. Results: Of the 35 patients included 23 had non-small cell lung cancer (NSCLC) and 12 patients had colorectal cancer (CRC) metastases. Compared to the 24-h post-ablation scan, at 24 months the median CT mass size had reduced to 51.1% from baseline. Based on mRECIST, at 12 months 84.8% showed partial response and 15.2% had stable disease. At 24 months 90% (n = 20) showed partial response whereas 5% had stable disease and another 5% showed complete response. A large proportion of patients were alive 12 months after MWA with a partial response based on mRECIST; this partial response rate had not changed at the 24 months mark. Conclusion: This study challenges the use of mRECIST for the assessment of therapeutic response of lung tumours treated with MWA suggesting that timelines, especially regarding the baseline scan and ablation characteristics, may need to be revised.