Significant advances in diagnostic and therapeutic interventions are required to help transform HCC from a disease often diagnosed late and restricted largely to palliative therapies to one diagnosed early where curative intent is the goal. Core to this is the elucidation of the molecular pathways operative in HCC pathogenesis. Histopathologic analysis and epidemiologic studies of HCC arising in the setting of cirrhosis have suggested multistep hepatocarcinogenesis through the identification of morphologically distinct precancerous lesions, including dysplastic foci and dysplastic nodules, and early small HCC (<2 cm).
135,
136 Yet the pathologic distinction between these types of lesions is often difficult and biopsies of small tumors carry a false-negative rate of 30%–50%.
137Recent expression profiles of human samples have suggested particular mRNA expression subsets, or signatures, associated with both improved diagnostic accuracy and lesion discrimination.
138–
141 For example, a 13-gene signature identified through high-throughput quantitative real-time polymerase chain reaction in 128 patient samples provided high diagnostic accuracy for HCC.
138 Additionally, the expression of three genes (
glypican 3,
lymphatic vessel endothelial hyaluronan receptor 1 and
survivin), has been reported to provide ~90% accuracy in distinguishing dysplastic nodules from early HCC.
139 Results of many of these genomic studies have been applied to more conventional immuno-histochemical analysis, and a recent prospective analysis of the protein expression of glypican 3, heat shock protein 70, and glutamine synthetase revealed 72% sensitivity and 100% specificity in detecting well-differentiated HCC in biopsy samples.
142 These markers have been validated in a larger number of patients and have recently been suggested as part of the diagnostic algorithm for the American Association for the Study of Liver Diseases.
37,
143Serum levels of several of these biomarkers have also been evaluated in diagnosis and surveillance, including glypican 3, des-gamma-carboxyl prothrombin (DCP), and
Lens culinaris agglutinin-reactive AFP, an isoform of AFP.
144–
147 While a recent study in a large population of patients with HCV-associated HCC suggested an improved sensitivity with a combination of AFP and DCP compared with either alone, to date additional serum biomarkers beyond AFP have not been incorporated in major HCC management guidelines.
55Radiographic imaging also plays a key role in the early diagnosis of HCC, and is critical for accurate staging and treatment-response assessment. The major difficulty in diagnostic imaging of the cirrhotic patient remains the accurate characterization of lesions less than 2 cm, and the incorporation of functional hepatic imaging and development of new contrast agents will likely improve the detection and characterization of these small tumors. Diffusion-weighted MRI has been shown to improve detection of HCC smaller than 2 cm, with sensitivities higher than multiphasic MRI alone, and represents a promising technique given its ease of implementation into current clinical practice.
148,
149The use of two new hepatocyte-specific gadolinium chelate contrast agents, gadobenate dimeglumine (Multihance; Bracco, Milan, Italy) and gadoxetic acid (Primovist; Schering, Berlin, Germany), with multiphasic contrast-enhanced MRI has been shown to improve in the diagnosis of HCC over MRI or CT alone.
150,
151 These agents have also been shown to enhance the differentiation of small HCCs (≤2 cm) from arterial-enhancing pseudolesions, common benign hepatic vascular lesions that mimic early HCC.
152,
153[18F]fluorodeoxyglucose positron emission tomography (FDG-PET) is limited by the varying degrees of FDG accumulation in primary HCC, and is not currently recommended in the diagnosis of HCC.
37,
38 While several studies have demonstrated a greater sensitivity for detection of distant metastasis with FDG-PET compared to CT, MRI, or radionuclide bone scan, its use is limited by high false-positive rates and it is currently not recommended by the AASLD or NCCN.
8,
37,
38,
154,
155 The use of new radiotracers, including [11C]acetate may, however, improve the sensitivity and specificity of PET scanning in the diagnosis and evaluation of HCC.
156Assessment of tumor response to nonsurgical treatments has traditionally been based on changes in tumor size and number, delineated by the World Health Organization and the Response Evaluation Criteria in Solid Tumors criteria.
157,
158 However, these criteria are often inadequate for the evaluation of HCC, particularly as it relates to novel molecular therapies, which often result in tumor necrosis.
159 Preliminary studies of both diffusion-weighted MRI and perfusion CT show promise in the evaluation of tumor response to both local ablative and systemic therapies.
160–
162Elucidation of signal transduction pathways implicated in tumorigenesis and development of targeted molecular therapies have fueled a revolution in oncology, and this has impacted the management of HCC directly with the demonstration of a significant survival advantage with the use of sorafenib. Given this success, the role of sorafenib alone and in combination with traditional locoregional therapies, systemic chemotherapy and novel molecularly targeted therapies is currently being investigated in various stages of disease ().
163 Additionally, alterations in several signal transduction pathways have been detected in HCC, including Wnt signaling, p53, insulin-like growth factor, Ras, epidermal growth factor receptor (EGFR), Akt/target of rapamycin (TOR), c-MET, VEGFR, and fibroblast growth factor (FGF).
164 This has resulted in the application of a myriad of new targeted therapies in both the preclinical and clinical setting, including the monoclonal antibodies bevacizumab (anti-VEGF) and cetuximab (anti-EGFR), and the small molecule inhibitors erlotinib (EGFR inhibitor), brivanib (FGF and VEGFR inhibitor), everolimus (mammalian TOR inhibitor) and linifanib (VEGFR and PDGFR inhibitor).
133 | Table 2Select phase III trials evaluating sorafenib |
Many of these therapies target well-established proteins that regulate critical aspects of tumorigenesis, including angiogenesis, proliferation, and survival. However, recent work has implicated microRNA dysregulation in many of these processes during hepatocarcinogenesis, and early studies of human HCC microRNA expression profiling have suggested expression signatures predictive of metastasis and survival.
165,
166 Epigenetic alterations, including DNA methylation and histone modification, have also been implicated in the pathogenesis of HCC.
164 Importantly, therapeutic interventions targeting some of these aberrant processes in the form of histone deacetylase inhibitors are currently being investigated in clinical trials of HCC.
163