Functional hepatic imaging as a biomarker of primary and secondary tumor response to loco-regional therapies

Objective criteria to measure tumor response are a key tenet for assessment of treatment efficacy when evaluating a therapeutic modality. Several response criteria have been proposed including the Response Evaluation Criteria in Solid Tumors (RECIST), modified RECIST (mRECIST), RECIST 1-1, and European Association for the Study of the Liver (EASL) guidelines. Response following loco-regional therapies (LRT) can be particularly difficult to assess as post-treatment changes may not always relate to changes in lesion size. As imaging modalities and solid tumor therapies continue to advance, there has been growing recognition that measurement of actual tumoricidal activity may not always be related to tumor size, and accurate assessment of treatment response may vary by therapeutic modality. As such, the objective change in the physical size characteristics of a tumor may not accurately reflect biological response to treatment. Functional imaging encompasses methods that are capable of detecting or measuring changes in tissue metabolism, blood flow, or composition. Conventional imaging modalities such as magnetic resonance imaging (MRI) and computed topography (CT) now include techniques such as diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC) maps, dynamic contrast enhancement (DCE-MRI), and perfusion CT (pCT). Use of functional cross-sectional imaging is particularly relevant to assess primary and secondary hepatic malignancies treated with LRT, such as trans-arterial chemoembolization (TACE), radiofrequency ablation (RFA), yttrium-90 (Y-90), and hepatic arterial infusion (HAI) chemotherapy. We herein review the imaging techniques, as well as the methodologies for measuring tumor response and survival, among patients treated with LRT for primary and secondary hepatic malignancies.