Editorial for “Characteristics and Early Recurrence of Hepatocellular Carcinomas Categorized as LR‐M: Comparison with Those Categorized as LR‐4 or 5”

Editorial for “Characteristics and Early Recurrence of Hepatocellular Carcinomas Categorized as LR-M: Comparison with Those Categorized as LR-4 or 5” Hepatocellular carcinoma (HCC) is the sixth most diagnosed cancer in the world and the fourth leading cause of cancer-related mortality. In the United States, the incidence and mortality of HCC have increased over the past four decades. The high-risk groups for HCC, such as positive hepatitis virus and alcoholic liver disease, have been established and the screening system is relatively well organized compared with the other types of cancers. A typical imaging finding of HCC is a hypervascular mass of increasing size with arterial phase hyperenhancement and washout appearance on dynamic contrast images in patients at high risk for HCC. In such cases, the diagnosis of HCC is made without histological confirmation, and treatment is initiated. However, the terminology of the imaging findings of HCC and diagnostic approach of HCC are not standardized, and it was necessary to establish uniformity in the terminology of imaging diagnosis in the diagnostic system to provide highspecificity diagnosis of HCC. Therefore, the American College of Radiology endorsed diagnostic criteria called the Liver Imaging Reporting and Data System (LI-RADS) for the diagnosis of HCC in high-risk groups. In LI-RADS, liver lesions, which are probable HCC and definitely HCC, are categorized as LR-4 and LR-5. The LI-RADS has been revised several times and the latest version is CT/MR LI-RADS V2018. Currently, LI-RADS has been incorporated into the American Association for the Study of Liver Disease (AASLD) guidelines for HCC and is becoming a standard diagnostic imaging method for HCC. Accordingly, various studies have been conducted on the validity and limitations of LI-RADS. Malignant tumors in the liver are not limited to HCC. For example, primary liver tumors include intrahepatic cholangiocarcinoma, and metastatic liver tumors include hepatic metastasis of colorectal cancer. In LI-RADS, liver lesions which are probably or definitely malignant but not specific for HCC are categorized separately as LR-M. In the case of LR-M, multidisciplinary discussion is recommended to determine individualized management and biopsy is often needed. Previous studies have shown that the prognosis of tumors classified as LR-M is worse than that of LR-4/5, and that the prognosis of HCC diagnosed as LR-M is also worse than that of LR-4/5. In this issue of JMRI, Shin et al compared single HCCs that underwent curative resection which are classified as LR-M with those classified as LR-4/5, and demonstrated that in the multivariate analysis, the LR-M category was an independent predictor for early recurrence and early recurrence rates were significantly higher in patients with LR-M HCCs than in patients with LR-4/5 HCCs. In addition, they revealed that LR-M HCCs showed poorer tumor differentiation than LR-4/5 HCCs in histopathological analysis. According to Shin et al, HCCs categorized as LR-M have more poorly differentiated histological types and a higher early recurrence rate. This result is meaningful because it implies that the LR-M category has the potential for distinguishing a poorly differentiated HCC from the typical well to moderately differentiated HCC. In this paper, a considerable number of HCCs classified as LR-M showed washout, nodule-in-nodule, and mosaic findings. Focusing on these findings, future studies may be able to develop criteria to distinguish poorly differentiated HCC from non-HCC malignancy in the group categorized as LR-M. If this could be achieved, LI-RADS would contribute not only to the imaging diagnosis of HCC, but also to the prediction of prognosis after treatment.