E D I T O R I A L

See referenced original article on pages 740–8,this issue.

Address for reprints: Raymond T. Chung, M.D., Gas-trointestinal Unit, GRJ 825, Massachusetts GeneralHospital, 55 Fruit Street, Boston, MA 02114; Fax:(617) 726-5895; E-mail: rtchung@partners.org

Received October 18, 2004; accepted October 26,2004.

Cytokine Polymorphisms andHepatocellular CarcinomaTo B or Not to B

Raymond T. Chung, M.D.

Gastrointestinal Unit, Massachusetts General Hospital, Boston, Massachusetts.

Hepatocellular carcinoma (HCC), one of the world’s most commonmalignancies, is responsible for over 1 million deaths annually.

The incidence of HCC is rising steadily, especially in countries inwhich chronic viral hepatitis is common. Worldwide, chronic infec-tion with hepatitis B virus (HBV) represents the most important causeof HCC.1

HBV, which is a member of the hepadnaviruses, is a partiallydouble-stranded DNA virus with a genome that contains four partiallyoverlapping open reading frames. These open reading frames encodethe pre-S1-S2-S, precore-core, polymerase, and X proteins. The pre-S1-S2-S gene product is processed to become hepatitis B surfaceantigen (HBsAg), and the secretion of HBsAg is emblematic of chronicinfection. In most patients, the precore-core gene product yieldssecreted HBeAg, a marker of active replication, which also can beconfirmed by molecular tests for circulating HBV DNA. HBV contrib-utes to hepatocarcinogenesis through several mechanisms. HBV, as aDNA virus, is capable of integration into host chromosomal DNA, inwhich random insertion adjacent to protooncogenes or tumor sup-pressor genes could activate proliferative pathways. In addition, theHBV X protein itself may be oncogenic.2 Most commonly, activereplication is associated with a necroinflammatory response, whichincreases hepatocyte necrosis, regeneration, and fibrosis and is asso-ciated with increased risk for the accumulation of mutations thatcontribute to malignant transformation.3 Finally, the development ofcirrhosis, which is the culmination of fibrosis accumulation, itself alsoappears to be associated with an increased risk for HCC. A recentlarge study from Taiwan found that the HCC risk was increased10-fold among HBsAg-reactive men who lacked HBeAg, that the HCCrisk was increased 60-fold among men who were reactive for bothHBsAg and HBeAg, and that this risk increased with age.4

The risk of developing persistent HBV infection is related directlyto the patient’s age at the time of exposure. Neonatal infection isassociated with chronicity rates exceeding 90%, whereas individualswho are exposed in adulthood experience virologic clearance rates� 95%. Among individuals from areas that are highly endemic forHBV, perinatal transmission accounts for the vast majority of infec-tions. Accordingly, the risk for HCC in these areas is the highest in theworld. However, even in those regions, only a minority of chronicHBV carriers will develop HCC, suggesting that host factors or other

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© 2005 American Cancer SocietyDOI 10.1002/cncr.20837Published online 7 January 2005 in Wiley InterScience (www.interscience.wiley.com).

environmental factors are important determinants ofthe risk for HCC.

The host immune response to HBV infection hasbeen characterized relatively well.5 CD4 cells recog-nize viral peptides in conjunction with major histo-compatability complex Class II molecules at the hepa-tocyte cell surface and release T-helper cell Th1 andTh2 cytokines. Th1 cytokines include interleukin 2(IL-2), interferon � (IFN-�), tumor necrosis factor �

(TNF-�), IL-12, and IL-18. These cytokines, in turn,lead to the activation of virus-specific CD8-positivecytolytic T lymphocytes, which effect clearance of vi-rally infected cells. Th2 cytokines include IL-4 andIL-10, which regulate Th1 cytokine production andlead to activation and differentiation of antibody-pro-ducing B cells. A reductionist model proposes thatexcess Th1 cytokine production leads to a net antiviralstate, whereas excess Th2 production tends to coun-teract the Th1 effect toward a less antiviral state.

Against this backdrop, the production of thesecytokines, of course, is governed not only by the en-gagement of CD4 cells by HBV-infected hepatocytesbut also by the intrinsic level of secretion of thesecytokines, which is determined in large measure at thelevel of individual gene expression. Thus, it is plausi-ble that, among chronically HBV-infected patientswho have high rates of HCC development, cytokineproduction is altered fundamentally compared withcytokine production among individuals do not de-velop HCC. Given such a scenario, an imbalance ofcytokines toward a less antiviral state may increaseviral replication and may lead to an increased fre-quency of events that produce malignant transforma-tion.

In this issue of Cancer, Nieters et al. tested thishypothesis.6 They performed a prospective case– con-trol study examining Th1 and Th2 genotypes amongchronic HBV carriers in a region of China known tohave one of the highest prevalence rates of HCC in theworld. From 1995 to 1998, 250 incident hospitalizedpatients with of HCC in southern Guangxi, China,were paired with contemporaneously admitted age-,gender-, and ethnicity-matched controls without HCCor cirrhosis. The great majority of patients, as ex-pected, were HBsAg-positive, whereas the great ma-jority of controls were HBsAg-negative. Cytokine ge-notypes were then assessed and classified as high-activity or low-activity, depending on associationsdescribed in the literature.

Nieters et al. found that the presence of eachpredicted low-activity Th1 genotype of IFN-�, IL-12,and IL-18 was associated with a nonsignificant risk forHCC; however, when the genotypes were consideredin composite fashion, the risk for HCC rose with in-

creasing numbers of low-activity genotypes. It shouldbe noted that this finding did not hold true for themajor Th1 genes IL-2 and TNF-�, which were distrib-uted comparably between cases and controls. An anal-ysis of the major Th2 genes IL-4 and IL-10 also re-vealed a significant trend for low-activity genotypesand an association with decreased risk for HCC. Takentogether, these findings suggest that individuals whohad the maximum number of low-activity Th1 genesand the minimum number of low-activity Th2 geneshad the highest (20-fold) relative risk for HCC com-pared with individuals who had no low-activity Th1genes and had at least 1 low-activity Th2 gene. Sub-group comparisons of cases and controls demon-strated that these cytokine-genotype associationswere even stronger among individuals who harboredchronic HBV infection compared with those who wereHBsAg-negative. Taken together, those findings impli-cate host genetic predispositions in the developmentof HBV-related HCC. Specifically, the finding of hostgenotypes collectively predicted to be associated withan attenuated cellular immune response appears to beassociated with higher rates of HCC. If these findingscan be confirmed, then they open up a potentially newarea of risk stratification for HCC.

However, these provocative findings beg severaladditional questions. First and most important, thereis the issue of genotype-phenotype correlation. Theprediction of a low-activity Th1 gene is not necessarilyborne out in direct testing of gene activity; because,potentially, there are many modifiers of gene expres-sion that cannot be predicted by gene testing, such asthe presence of other unrecognized gene polymor-phisms that compensate for the predicted activity.Thus, it would be important to correlate diminishedIFN-� or IL-4 release from lymphocytes in individualswho have low-activity polymorphisms using func-tional assays. Such a correlation would strengthen themechanistic underpinning of the association.

Perhaps even more important, if, in fact, the pres-ence of multiple low-activity Th1 genotypes and fewlow-activity Th2 genotypes is associated with dimin-ished host-immune control of virus, then this shouldbe reflected in measurements of viral control. There-fore, it would have been of interest to know the rep-licative status of HBV among the patients surveyed. Ifhigh HBV DNA levels and HBeAg status in fact docorrelate with the genotypes associated with dimin-ished immune control, then the prediction may bevalidated. The polymorphisms would then help to ex-plain who among chronic carriers would be prone toHBV replication. Indeed, other studies have correlatedlow-activity IFN-� polymorphisms with risk of chronicHBV infection.7 Thus, HBV replication itself may be

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the dominant factor driving hepatocarcinogenesis, inthat a persistent inflammatory state (albeit blunted) inthe face of ongoing replication is a greater risk fortransformation than the more robust immune re-sponse that succeeds in keeping HBV in an inactivecarrier state. This prediction squares with the ob-served finding of higher HCC risk in HBeAg-positiveindividuals.4 The utility of gene testing for these poly-morphisms, then, may lie more in identifying thosewho are at risk for replicative disease than those whoare at risk for HCC per se.

Although it may appear attractive to stratify pa-tients who have perinatal HBV for subsequent risk ofreplication and HCC risk, it remains doubtful that anysingle genotype or combination of genotypes will doso with absolute sensitivity and specificity. Thus, therecommendation to monitor HBsAg-positive individ-uals for the development of HBV replication, whichcan occur spontaneously at any time during the life ofa carrier, would appear unlikely to change. The inten-sity of that monitoring, however, may be influencedsubtly if the findings from Nieters et al.6 can be con-firmed. For instance, a high-activity Th1 and low-activity Th2 genotype may require even less intensivemonitoring than that already practiced for HBsAg-positive, inactive chronic carriers. Whether monitor-ing practices change or not as a result of genotyping,

the mandate that replicative HBV disease must betreated because of the long-term risk for necroinflam-matory disease, fibrosis, cirrhosis, and HCC remainsfirmly in place. Ultimately, it will be the introductionof ever-improving antiviral chemotherapy againstHBV that represents our best weapon against hepato-carcinogenesis.

REFERENCES1. Donato F, Boffetta P, Puoti M. A meta-analysis of epidemi-

ological studies on the combined effect of hepatitis B and Cvirus infections in causing hepatocellular carcinoma. Int JCancer. 1998;75:347–354.

2. Bouchard MJ, Wang LH, Schneider RJ. Calcium signaling byHBx protein in hepatitis B virus DNA replication. Science.2001;294:2376 –2378.

3. Nakamoto Y, Guidotti LG, Kuhlen CV, Fowler P, Chisari FV.Immune pathogenesis of hepatocellular carcinoma. J ExpMed. 1998;188:341–350.

4. Yang HI, Lu SN, Liaw YF, et al. Hepatitis B e antigen and therisk of hepatocellular carcinoma. N Engl J Med. 2002;347:168 –174.

5. Rehermann B. Immune responses in hepatitis B virus infec-tion. Semin Liver Dis. 2003;23:21–38.

6. Nieters A, Yuan J-M, Sun C-L, et al. Modifying effects ofcytokine genotypes on hepatitis B virus-related hepatocel-lular carcinoma. Cancer. 2005;103:740 –748.

7. Ben-Ari Z, Mor E, Papo O, et al. Cytokine gene polymor-phisms in patients infected with hepatitis B virus. Am JGastroenterol. 2003;98:144 –150.

656 CANCER February 15, 2005 / Volume 103 / Number 4