Primary liver cancer response can be evaluated by a number of competing response criteria, using CT or MRI, as well as advanced MR imaging techniques. The learning objectives for this course are: to recognize the commonly used therapies for HCC, to compare response criteria used in therapeutic trials, and to apply the new LI-RADS Treatment Response Algorithm.
The assessment of treatment response can affect the approval of therapeutic interventions aimed towards hepatocellular carcinoma (HCC), the most common primary liver cancer, as well as intrahepatic cholangiocarcinoma (ICC). As the number of available therapies for HCC and ICC have proliferated, so has the number of response criteria. In addition, numerous investigators have explored the role of advanced MR techniques, including the use of diffusion weighted imaging (DWI), dynamic contrast enhancement (DCE)-MRI, and volumetric analysis, to further predict the outcome of HCC patients. Unfortunately, there is little guidance for diagnostic radiologists on how to choose between competing criteria and imaging modalities to evaluate HCC response in daily clinical practice. Furthermore, comparing the effectiveness of locoregional or systemic therapies against each other becomes problematic. The learning objectives for this course are: to recognize the commonly used therapies for HCC, to compare response criteria used in therapeutic trials, and to apply the new LI-RADS Treatment Response Algorithm.
Locoregional therapies for HCC have proliferated in recent years, but can be roughly divided into locoablative and transcatheter directed therapies. Examples of locoablative therapies include: ethanol ablation, radiofrequency ablation, microwave ablation, and cryoablation. Transcatheter therapies can be performed with bland embolization, or various forms of transarterial chemoembolization and radioembolization. Unlike systemic therapies, the effects of locoregional therapy are often immediate, with prominent changes in vascularity and enhancement of the targeted tumors. Thus, measurements of change in enhancing tumor after therapy is often used as evidence for treatment effect, and forms the basis for response criteria such as mRECIST (modified Response Evaluation Criteria in Solid Tumors).
mRECIST has shown promise as a formal modification of RECIST for assessment of HCC both after locoregional and systemic therapies. RECIST is based on unidimensional measurements of target lesions (i.e. tumors), which usually decrease in size in patients who respond to systemic therapy. However, with locoregional therapy, HCC de-enhancement can occur without corresponding tumor shrinkage and the number of responders benefiting from therapy may be underestimated with RECIST compared to mRECIST. Ultimately, for tumor response criteria to be meaningful, they must act as surrogate reference standards for patient benefit as measured by prolongation of survival. This is why the barrier to adoption remains high for mRECIST and for other response criteria, including functional MR imaging criteria based on DWI and DCE-MRI. Their adoption will depend on the level of evidence (ideally, response criteria should be evaluated in multicenter placebo-controlled clinical trials as opposed to single center retrospective single arm studies), and the reproducibility of each criterion.
While mRECIST is still being evaluated as a response criteria in HCC clinical trials, its use in daily clinical practice is cumbersome for diagnostic radiologists. The Liver Imaging Reporting and Data System (LI-RADS) Treatment Response Algorithm was thus created to address the clinical gap in reporting individual observations after locoregional therapy, using CT or MRI. While similar to mRECIST, with the use of one-dimensional tumor measurements of enhancing tumor, LI-RADS expands the imaging criteria for viable disease beyond arterial phase hyperenhancement. Case examples will be used to illustrate the LI-RADS Treatment Response Algorithm for HCC after locoregional therapy.
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