Biomed Imaging Interv J 2006; 2(3):e7
© 2006 Biomedical Imaging and
Chronic hepatitis B infection and liver cancer
CH Wong, MBBS, MMed, MRCP,
KL Goh, MBBS, FRCP, FACG
Department of Medicine, Faculty of Medicine, University of Malaya,
Kuala Lumpur, Malaysia
Hepatitis B virus (HBV) is one of the most well recognised
human carcinogens. Since its discovery about 40 years ago, HBV has been studied
extensively. This article summarises the evidence derived from various studies
including epidemiological, animal model, histopathology studies and molecular
genetics studies leading to the establishment of HBV as the main aetiological
agent for hepatocellular carcinoma (HCC). The reduction in the incidence of
childhood HCC due to mass hepatitis B vaccination in Taiwan is a dramatic
demonstration of the critical aetiological role of hepatitis B in HCC. Thus it
is essential for interventionalists to understand the epidemiological and
pathogenesis of HCC to ensure optimal patient care. � 2006 Biomedical Imaging
and Intervention Journal. All rights reserved.
Keywords: Chronic hepatitis B infection, hepatocellular
Hepatocellular Carcinoma (HCC) is one of the most common
cancers affecting Asians. In the overwhelming majority of cases, it is
associated with chronic hepatitis B infection [1,2], which appears to be the
cause of 50% to 60% of HCC worldwide . Other recognised causes of HCC are
chronic hepatitis C infection, alcoholic liver disease and other chronic liver
diseases, which can lead to liver cirrhosis. HCC is a late complication of
chronic hepatitis B infection that usually occurs at the fourth and fifth
decade of life especially when the patients are older or liver cirrhosis has
developed. The aim of this review is to provide the available evidence
demonstrating the causal link between chronic hepatitis B infection and HCC.
Ecological Comparison Studies
The earliest epidemiological studies have shown that areas
with a high prevalence of hepatitis B infection were also areas with the
highest incidence of HCC (Table 1) [4,5]. For example, countries in the East
Asian region - China, Taiwan, Korea and Japan where the prevalence rate of
hepatitis B infection is very high, were also areas with the highest incidence
of HCC. The burden of HCC in this region in fact, constitutes about 66% of the
total number of HCC cases worldwide . The risk factor for the high incidence
of HCC in this area is hepatitis B infection where the attributable risk from
this viral infection ranged from 40% to 90% .
Table 1 Prevalence of hepatitis B and incidence of liver cancer.
Another interesting observation which is closely related to
the above observations is the preponderance of HCC amongst certain ethnic
groups with a high prevalence of hepatitis B infection. This observation is
well seen in the multiethnic countries of Southeast Asia of Malaysia and Singapore
where three major Asian races have co-existed for more than two generations. In
these countries, the Chinese have the highest incidence of HCC and the highest
prevalence of hepatitis B infection compared with the Malays and Indians who
have a much lower prevalence of hepatitis B infection .
Longitudinal Cohort Follow-up Studies
Longitudinal cohort follow-up studies have provided the most
persuasive evidence supporting the causal association between HBV infection and
HCC. Beasley et al conducted one of the largest epidemiological studies
so far, involving 22,707 Chinese male civil servants in Taiwan . Three
thousand four hundred and fifty four patients or 15.2% of the study population
were HBsAg-positive. The initial results from this extensive study were
published in 1981 after a mean duration of 3.3 years follow-up constituting
75,000 man-years follow-up. During this period of follow-up, there were 307
deaths, 41 due to primary HCC and 19 due to liver cirrhosis, which accounted
for 19.5% of the total deaths. Of the 41 patients who died of HCC, 40 were HBsAg-positive
and only one was HBsAg-negative. This gave rise to a highly significant
calculated relative risk of 223 among patients who were HBsAg-positive and
dying of primary HCC. Among the 19 patients who died of liver cirrhosis, 17 of
them were HBsAg-positive. The HBsAg-positive status was therefore significantly
associated with a marked increase in the incidence of death due to HCC and
A further follow-up review in 1986 with approximately
202,000 man-years of follow-up at an average of 8.9 years per man showed a
further 161 cases of HCC. One hundred and fifty two cases were HBsAg-positive,
giving rise to an incidence of HCC of 494.5 per 100,000 population per year
among HBsAg carriers compared with 5.3 among the non-HBsAg carriers. The
relative risk of HCC among HBsAg-carriers compared to non-HBsAg carriers for
this data was 98.4 (95% CI=50.2 to 193) .
This Taiwan prospective study provided the strongest
evidence of the role of chronic HBV infection as an aetiological agent in the
causation of HCC.
Effect of mass vaccination on liver cancer incidence
rates in children
With the identification of HBV infections as a major aetiological
factor in HCC, a nationwide hepatitis B vaccination program was implemented in
Taiwan, the first such program worldwide in1984. Within 10 years, this program
had successfully reduced the HBV carrier rate in children from 10% to 1%. The
implementation of such a comprehensive vaccination program in Taiwan has
allowed important epidemiological observations to be made with respect to the
incidence of HCC.
In Taiwan, the association of HBV and HCC is stronger in
children than in adults. The rate of seropositivity for HBV nearly approached
100% in children with HCC as compared to 70% to 80% in adults. Although, the
incidence of childhood HCC is low worldwide, the incidence of HCC in Taiwan is
relatively high and therefore, any changes in the incidence rate would be
easier to detect and measure.
In 1994, Chang et al  studied the impact of
universal hepatitis B vaccination in Taiwan on the incidence of HCC in
children. In general, the incidence of HCC in children aged six to 14 years old
showed a declining trend from 1981 to 1994. It was reported that the average
annual incidence of HCC in these children between 1981 and 1986 was 0.70 per
100,000 children (range, 0.65 to 0.78). The incidence declined to 0.57 per
100,000 children (range, 0.48 to 0.62) between 1986 and 1990. This rate further
dropped to 0.36 per 100,000 children (range, 0.23 to 0.48) between 1990 and
1994. This reduction in the annual incidence rate was highly significant
statistically (p<0.01). The reduction in cancer incidence was seen with HCC
only, while the annual incidence of other childhood cancers during this period
remained similar indicating that the change in HCC incidence must be
specifically related to the change in the prevalence of hepatitis B infection
rather than a general change in the environment or living conditions. In
addition, the reduction in the incidence of liver cancer was seen only in
children aged six to 14 years old whereas the incidence remained unchanged in
children aged up to five years old, in whom the aetiology of liver cancer was
due to hepatoblastoma rather than hepatitis B infection (Figure 1).
Figure 1 Comparison of the Incidence
of Liver Cancer in Children 6 to 14 and 0 to 5 Years of Age,
According to Birth Cohort  (reproduced with kind permission).
The wood chuck hepatitis virus has similar characteristics
with the human hepatitis B virus and provides an excellent animal model to
study the pathogenesis of HCC. In the wild, animals infected with the woodchuck
virus (WHV) have been shown to develop liver cancer. In experimental
conditions, inoculation of a high dose of WHV results in the development of HCC
in almost 100% of the animals. Laboratory studies have shown integration of the
WHV DNA with the woodchuck hepatocyte DNA. The woodchuck model demonstrates to
us that liver cancer can develop following a viral infection of the liver. [12,
HISTOPATHOLOGY STUDIES IN HUMANS
Scientists had postulated the association between HBV and
HCC based on ecological comparison studies but were initially unable to
demonstrate the virus within the HCC tissue until 1970s when a Japanese
pathologist, Shikata, developed a histochemical stain called orcein stain ,
which could stain the HBsAg within the tissue and thereby allowing the
identification of the virus in liver tissue. Subsequently, more sophisticated
staining methods were developed such as immunoperoxidase technique and indirect
immunofluorescence. These new techniques allowed scientists to study the
association of HBV and HCC in greater depth. Many such studies have been
published since then. One study done in Singapore  showed orcein-positive
liver cells in 37 out of 50 (74.0%) cases of HCC, and only five out of 113
(4.4%) in the control group. In addition, there was also a significant
difference in the frequency of HCC in orcein-positive and orcein-negative
cirrhotic livers (28 out of 50 and 10 out of 40 respectively). Akagi et al
 from Japan analysed 105 autopsy cases of HCC and found that HBsAg was
detected with the orcein stain in 58 cases (55.2%) compared with four out of
171 cases (2.3%) of control group. These results demonstrated a close
association between HBV and HCC.
Further evidence derived by using molecular studies has
strengthened the causal relationship of HBV and HCC. It has been demonstrated
that the incorporation of certain viral particle such as HBV DNA into the host
genome can act as a precursor to HCC. The viral double stranded DNA encodes
four types of genes i.e. surface gene for HBsAg, core gene for HBcAg,
polymerase gene for HBV DNA and X gene for HBxAg. HBsAg, HBcAg, HBV DNA and HBxAg
all have been found within HCC tumour in the tissue specimen. HBV DNA occurs
mainly in two forms of infected hepatocytes, the covalently closed circular (ccc)
DNA and the integrated DNA. The cccDNA serves as the template for host RNA
polymerase II, which initiates the production of HBsAg, HBcAg, viral DNA
polymerase and HBxAg. Whereas the integrated DNA predominates in HCC cell
nuclei and has been shown in several studies to contain enhancers that may
modulate several liver specific genes, transcriptional activators and
alteration of the X gene functions. Although the actual mechanisms of hepatocarcinogenesis
remain unclear, HBxAg have been implicated as the most important viral product
that cause direct malignant cell transformation in the pathogenesis of HCC.
Several in vitro studies have shown the effects of HBxAg on cellular repair,
proto-oncogenes, tumour suppressor gene, anti-apoptotic pathway and the
induction of HCC in transgenic mice. These evidence support the probable direct
effect of a HBV component, HBxAg, in the development of HCC [17-24].
The causal link between chronic hepatitis B infection and
HCC is irrefutable. With mass vaccination at birth in place in most countries
in Asia, and improved socio-economic conditions, the prevalence of hepatitis B
infection will steadily decline. In countries where this has happened such as
in Japan, hepatitis B is now the main �cause� of HCC as in the West. At
present, however, hepatitis B remains prevalent in Asia and prevention will
continue to result in marked decrease in the incidence of HCC.
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|Received 14 October 2005; received in revised form 16 December 2005; accepted 11 January 2006
Department of Medicine, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia. Fax.: +603-79556936; E-mail: firstname.lastname@example.org (Choon-Heng Wong).
Please cite as: Wong CH, Goh KL, Chronic hepatitis B infection and liver cancer, Biomed Imaging Interv J 2006; 2(3):e7
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