Moving Away from Uncertainty: A Potential Role for Ancillary Features in LI-RADS Treatment Response.

T response assessment guides the care of patients with hepatocellular carcinoma (HCC) after local-regional therapy (LRT). While Response Evaluation Criteria in Solid Tumors (RECIST), version 1.1, remains the standard for response assessment after systemic therapy, LRT of HCCs can be performed over multiple sessions, does not target every lesion equally, and often induces tumor necrosis without concurrent change in tumor size. Thus, response to LRT is better assessed by recognizing changes in tumoral enhancement pattern. Modified RECIST (mRECIST) was introduced in 2010 and adapted the concept of viable tumoral tissue showing uptake of contrast material in the arterial phase of CT or MRI (1). The Liver Imaging Reporting and Data System (LI-RADS) Treatment Response (LR-TR) algorithm was subsequently developed to standardize interpretation and reporting of LRT-treated HCC. Although the LR-TR algorithm adopts HCC enhancement pattern–based assessment, it expands on mRECIST by adding features of washout and enhancement similar to pretreatment as imaging findings supportive of HCC viability after LRT (2). Furthermore, the LR-TR algorithm allows an observation to be categorized as equivocal if tumor viability is unclear. While the LR-TR algorithm remains a newcomer compared with mRECIST, the evidence supporting its categories of LR-TR viable, LR-TR equivocal, and LR-TR nonviable has been building since its introduction in 2017 (3). The LR-TR viable and LR-TR nonviable categories offer clear feedback to the treating physician about HCC response to targeted therapy. The use of the LR-TR equivocal category, however, generates ambiguity because imaging findings are not always clearly in favor of tumor viability or nonviability. For example, in a few scenarios, such as early posttransarterial radioembolization or external beam radiation therapy, HCC gradually decreases in enhancement as radiation necrosis develops. Early imaging followup in these cases can be challenging to assess, as persistent enhancement is seen for many months. While this category generates uncertainty, the LI-RADS Tumor Response Working Group agreed to acknowledge the possibility of equivocal imaging findings after treatment. It is worth noting that RECIST indirectly includes the concept of equivocation in its response criteria. Specifically, the RECIST guidelines define how to recognize “unequivocal progression of existing non-target lesions. ” For HCCs treated with ablation or intra-arterial therapy, recent studies have shown that most LR-TR equivocal lesions contain viable tumor at histopathology (4–6). In addition, it has been shown that there is an improvement in sensitivity with a minimal decrease in specificity if the LR-TR equivocal lesions are considered equivalent to LR-TR viable lesions (4–6). In this issue of Radiology, Park et al (7) investigated the diagnostic performances of the LR-TR algorithm and a modified version of the algorithm in a cohort of 138 patients with HCC. Park et al evaluated whether adding ancillary features to MRI improved the prediction of tumor viability compared with that with the conventional enhancement pattern–based LR-TR algorithm on CT or MRI scans. They found that the use of ancillary features increased their sensitivity to detect viable disease to 84% (from 76% on MRI scans with the conventional LR-TR algorithm) without sacrificing specificity (80% vs 83%). Pathologic necrosis confirmed via liver explantation or surgical resection was their reference standard. Their results are comparable with those of a recent study that similarly evaluated the added value of ancillary features to the LR-TR algorithm (8). In that study, Kim et al found an Moving Away from Uncertainty: A Potential Role for Ancillary Features in LI-RADS Treatment Response