Background: Data comparing EASL and mRECIST criteria for response evaluation in treatment of hepatocellular carcinoma are rare. We evaluated inter-observer variability by these two response evaluation criteria in treatment-naïve patients undergoing chemoembolization. Methods: For 133 patients undergoing chemoembolization, two radiologists independently measured sum of bi-dimensional and uni-dimensional diameters at baseline using both EASL criteria and mRECIST, and their changes on first follow-up for up to 5 target lesions. Results: Concordance correlation coefficients for sum of bi-dimensional and uni-dimensional diameters at baseline between two observers were 0.992 and 0.988, respectively. However, those for their changes on follow-up were 0.865 and 0.877, respectively. Similarly, mean differences in sum of bi-dimensional and uni-dimensional diameters at baseline between two observers were small; -0.455 and 0.079. cm, respectively. However, mean differences in changes (%) in sum of bi-dimensional and uni-dimensional diameters on first follow-up between observers increased by -9.715% and -9.320%, respectively. Regarding tumour numbers, kappa-value between observers was 0.942. For treatment response (complete or partial response, stable disease and progression), kappa-value was 0.941 by both criteria. When only up to two target lesions were assessed, kappa-value was 1.000 by both criteria. Conclusions: Inter-observer agreements using both response evaluation criteria were excellent, especially when up to two targets were assessed.
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