ReviewPrognostic molecular markers in hepatocellular carcinoma: A systematic review
Introduction
Hepatocellular carcinoma (HCC) is the 5th commonest malignancy worldwide and is the third most common cause of cancer-related death. Although the prevalence is highest in Africa and Asia, the incidence in western countries is rising, mainly due to increasing rates of alcoholic liver disease and hepatitis C infection. HCC most commonly develops in patients with chronic liver disease, the aetiology of which includes alcohol, viral infection (hepatitis B and C), metabolic diseases (haemachromatosis, α-1-antitrypsin deficiency) and aflatoxin. Surgery, including transplantation, remains the only curative modality for HCC. However, the long-term prognosis of patients undergoing potentially curative hepatic resection is still poor, with reported 5-year survival rates ranging from 17% to 53%. Despite resection with curative intent, the clinical course is variable and recurrence occurs in a high proportion of cases.1, 2
The ability to predict patients at higher risk of recurrence and with a poor prognosis would help to guide surgical and chemotherapeutic treatment according to individual risk. Attempts have been made to predict recurrence and poor prognosis in patients with HCC after hepatectomy using clinicopathological characteristics. Tumour grade, size of tumour, microvascular invasion, portal vein tumour thrombus and the presence of microsatellite lesions have all been found to predict survival.3, 4, 5, 6, 7 These, however, lack sensitivity for accurately predicting individual prognosis. Serum tumour markers, particularly alpha fetoprotein (AFP), have also been found to be prognostic;5 however, they rely on a significant tumour burden making their usefulness in operable tumours questionable. More recently, interest has been focused on the prognostic value of serum inflammatory markers as a reflection of the host response to the tumour. In particular, an elevated preoperative serum C-reactive protein (CRP) has been found to be associated with a 75% recurrence rate at 12-months following resection for HCC, as well as being associated with reduced disease-free and overall survival when compared to patients with a lower preoperative level.8
With advances in understanding of tumour biology, interest in molecular biomarkers of carcinogenesis has grown, both in terms of their prognostic significance and also their potential as therapeutic targets. Table 1 summarises the molecular markers which have been shown to play a role in hepatocarcinogenesis. For detailed information regarding these markers, the reader is referred to recent reviews of molecular pathways involved in HCC, particularly in relation to their association with the different aetiological risk factors for HCC.9, 10, 11 The aim of this review was to examine the current knowledge regarding the prognostic role of these molecular biomarkers in HCC. A systematic literature review was performed of the available evidence for the role of molecular biomarkers on the prognosis of patients undergoing resection of HCC. Searches of the Pubmed, MEDLINE, and Web of Science databases were performed using the following keywords, in varied combinations: hepatocellular carcinoma, liver, hepatic, resection, hepatectomy, recurrence, prognosis, molecular markers and biomarkers. Individual biomarkers were also included in searches. Cited references in articles identified were used to find further relevant publications. The search was restricted to English Language publications and was conducted up to 31st October 2006. Studies published in abstract form only, unpublished studies and articles published in non-peer reviewed journals were not included. Animal and in vitro work were also excluded. Studies of molecular markers solely in unresectable HCC were also excluded. Prognostic value of the following molecular markers is discussed: tumour suppressor genes; oncogenes; cell cycle regulators; apoptotic regulators; markers of angiogenesis; markers of invasion and metastasis; growth factors and receptors; proliferation indices; telomerase; and markers of genomic instability.
Section snippets
p53
The p53 tumour suppressor gene is located on chromosome 17p13.1 and is responsible for regulation of the cell cycle at the G1/S and G2/M interfaces, as well as induction of apoptosis in response to severe damage to cellular DNA. p53 has been found to be mutated in 24–69% of HCC.12, 13, 14 Mutations of p53 result in unregulated replication of defective DNA, genomic instability and progression to cancer. Wild-type p53 has a short half-life and is therefore undetectable by immunohistochemistry
Oncogenes
The c-met and c-myc oncogenes have both been assessed for their prognostic significance in HCC. c-met is commonly over-expressed by HCC, and has been associated with reduced overall survival in the only prognostic studies performed.30, 31 c-myc expression has been found to be increased in those patients developing early recurrence post-hepatectomy,32 and amplification of the c-myc gene has been associated with reduced disease-free and overall survival following resection.33, 34
Cyclin and cyclin-dependent kinases
The G1/S transition is important for cell cycle progression. Phosphorylation of Rb by cyclin/cyclin-dependent kinase complexes inactivates it, allowing cell cycle progression. Over-expression of cyclin A, D1 and E have all been investigated for prognostic significance following resection of HCC. Chao and colleagues35 found cyclin A expression to independently predicted decreased disease-free survival on multivariate analysis. Two studies have found elevated cyclin D1 expression to be associated
Bcl-2 family
The Bcl-2 family is one of the best-characterised groups of apoptosis-mediating factors. Amongst the members of this family, Bax, Bak and Bcl-xS act as promoters of apoptosis, with Bcl-2 and Bcl-xL acting as apoptotic inhibitors. Several of these have been investigated for prognostic significance following resection for HCC. Bcl-2 expression was not found to be associated with prognosis following resection.54 However, Bcl-xL over-expression has been found to independently predict decreased
Microvessel density
Microvessel density (MVD) is a commonly used index of angiogenesis in tumours, involving immunohistochemical staining of endothelial cell markers. Commonly used markers include CD34, CD31 and von Willebrand factor (vWF). MVD using CD34 has been found to be independently prognostic for decreased disease-free survival on multivariate analysis in patients undergoing resection of HCC under 5 cm in size.60, 61 Another study found CD34 to predict decreased overall survival on multivariate analysis.62
Matrix metalloproteases
The matrix-degrading metalloproteinases (MMP) are a family of proteolytic enzymes characterised by their ability to degrade the extracellular matrix, and are considered to play an important role in cancer invasion and metastasis. Elevated levels of MMP-2 (gelatinase A), a MMP which degrades collagen IV, a chief component of the basement membrane, have been found in patients who suffered recurrence post-resection88 and to be associated with early recurrence.89 Concomitant over-expression of
Transforming growth factor-β
Transforming growth factor betas (TGF-βs) belong to a superfamily of polypeptide signalling molecules involved in regulating cell growth, differentiation, angiogenesis, invasion and immune function. TGF-β1 is the predominant form in humans, promoting angiogenesis and suppressing immune function. Higher expression of TGF-β1 has been found to be an independent prognostic factor for reduced survival in patients with inoperable HCC.98 However, the only study investigating the prognostic value of
Proliferation indices
The proliferative activity of a tumour provides an indication of its rate of growth and correlates with an aggressive phenotype. Proliferation may be assessed by mitotic index, S-phase cell fraction, or immunohistochemical assessment of proliferation-associated nuclear proteins (Ki-67, its epitope MIB-1, proliferating cell nuclear antigen (PCNA) or argyrophilic nucleolar organizer regions (AgNOR)). A higher mitotic index has consistently been found to predict decreased disease-free and overall
Telomerase
Human telomerase is a ribonuclear protein composed of telomerase RNA and human telomerase reverse transcriptase (hTERT). Shortening of telomeres in human cells to a critical length limits the growth to a finite number of divisions before senescence or cell death occurs and it is thought that telomerase activation stabilises telomere length, preventing this. In patients with HCC, studies investigating the prognostic value of telomerase activity have found high telomerase activity, as assessed by
Chromosomal instability/aneuploidy
Aggressive tumours are characterised by genomic instability which is thought to favour cancer progression and adaptation. Chromosomal instability (CIN) is the loss or gain of a chromosomal segment during cell division. As in other human malignancies, HCC demonstrates a high incidence of CIN. CIN leads to an increase in aneuploidy, which in turn drives further mutations, enhancing tumour progression. Two studies have used array comparative genomic hybridisation (aCGH) to assess the prognostic
Conclusions
Research into the molecular biology of hepatocarcinogenesis has identified a multitude of molecular biomarkers with potential prognostic significance. Markers of particular interest include p53-mutation, PTEN, c-met, c-myc, p18, p27, p57, serum VEGF, HIF-1α, MMP-2, -7, and -12, as well as proliferation indices, telomerase activity and aneuploidy (Table 1). The majority of studies have focused on individual markers in retrospective studies, and differing methodologies between studies may explain
Conflict of interest statement
None declared.
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