LI-RADS Version 2018 Treatment Response Algorithm: The Evidence Is Accumulating.

I 2017, the Liver Imaging Reporting and Data Systems (LI-RADS) was updated to include a treatment response algorithm (TRA) (1), which did not undergo modification in the 2018 LI-RADS update (2,3). In patients with hepatocellular carcinoma (HCC), the TRA offers diagnostic radiologists a standardized approach to assess tumors and report their response after local-regional therapy (4). According to the LI-RADS TRA, treated HCC can be classified as LI-RADS treatment response (LR-TR) viable, LR-TR equivocal, or LR-TR nonviable, based on the posttreatment enhancement pattern. The TRA is modeled after the modified Response Evaluation Criteria in Solid Tumors (mRECIST) (5), which is primarily based on the recognition of arterial phase hyperenhancement. However, the TRA differs by including an LR-TR equivocal category and an expansion of the imaging criteria for tumor viability, such as the inclusion of washout appearance. Unlike the patient-level response provided by mRECIST, the LIRADS TRA aims to categorize individual lesion viability to help guide future local-regional interventions. However, as a newer algorithm for HCC treatment response, it needs further validation to ensure that the response categories accurately reflect tumor viability after local-regional therapy. In this issue of Radiology, Chaudhry et al assessed the performance of the LI-RADS TRA in 36 patients with 53 lesions who were undergoing ablative therapy prior to liver transplantation to predict complete necrosis as compared with a histopathologic reference standard (6). When LRTR equivocal was treated as equivalent to LR-TR nonviable, sensitivity in the prediction of viable tumor ranged from 40% to 77% across readers. When LR-TR equivocal was treated as LR-TR viable, the sensitivity increased to 81%–87%. The specificity in the prediction of complete tumor necrosis ranged from 85% to 97% and from 81% to 85%, respectively, based on the same two scenarios. These results are comparable to those reported by two separate studies evaluating the LI-RADS TRA in patients with HCC undergoing predominantly transarterial embolization or chemoembolization (7,8). The necessity of the LR-TR equivocal category has often been questioned, but its inclusion reflects the decision by the LI-RADS Tumor Response Working Group to allow some uncertainty in the assessment of treatment response. Chaudrey et al assessed a minority of the lesions as LR-TR equivocal after local ablative therapy by consensus reading (six of 53 lesions [11%]); of the six LR-TR equivocal lesions, five (83%) were incompletely necrotic at histopathology. On the other hand, Shropshire et al used the LR-TR equivocal category more frequently in patients treated with transarterial embolization (17 of 63 [27%]); of the 17 LRTR equivocal lesions, 12 (71%) were incompletely necrotic at histopathology (7). Seo et al used the LR-TR equivocal category less frequently (59 of 287 [21%]), with most demonstrating some tumor viability at pathology (53 of 59 [90%]) (8). Taken together, these studies suggest that many treated lesions categorized as LR-TR equivocal harbor some viable tumor at histopathology, and the impact of folding the LR-TR equivocal category into the LR-TR viable category may yield higher sensitivity with a minimal loss in specificity. Whether the LR-TR equivocal category should be eliminated altogether requires further study, including an evaluation of its role in other local-regional therapies, such as radioembolization. In clinical practice, patients with treated HCC classified as LR-TR equivocal should be monitored closely for interval progression. The ability of the LR-TR algorithm to allow us to predict complete tumor necrosis remains limited. In Chaudhry et al and Shropshire et al, less than half of LI-RADS Version 2018 Treatment Response Algorithm: The Evidence Is Accumulating