Kaposi sarcoma-associated herpesvirus
This section contains information on Kaposi sarcoma-associated herpesvirus (KSHV) including Kaposi sarcoma, Primary effusion lymphoma and Multicentric Castleman's Disease.
Kaposi sarcoma-associated herpesvirus (KSHV, also known as HHV8) is more closely related to Epstein-Barr virus (EBV) than it is to other human herpesviruses, but it has its own unique complement of latent cycle genes1,2 (Figure 5.1).
Like EBV, it preferentially infects and establishes latency in B lymphocytes, but its effects in B cell growth are more subtle. The virus also infects, and can replicate in, certain types of endothelial cells. Quite unusually for a human herpesvirus, KSHV prevalence varies widely in different human populations. More than 50% people in many African countries carry KSHV, but this falls to 10% or less in Eastern European/Mediterranean countries and < 1% in Northern Europe3. The circumstances under which KSHV infection leads to cancer strongly indicate that a fine balance exists between this potentially dangerous virus and the host's immune defences 4,5.
Kaposi Sarcoma
Classic Kaposi sarcoma (KS) was first described as a slow-growing endothelial cell tumour seen in elderly men of Mediterranean or Eastern European descent; subsequently a slightly more aggressive form of the disease (so called 'endemic' KS) was recognised at higher rates in African populations. With the onset of the AIDS epidemic the worldwide incidence of this cancer has increased dramatically in the past 25 years, and a much more aggressive form of KS is now the commonest tumour among HIV-infected people in Africa (Figure 5.2). KS also became common among a subset of HIV patients in the West, but the incidence is now falling with the introduction of effective anti-HIV drug therapy. KS is also appearing among the small proportion of transplant recipients who happen to be infected with KSHV; this clearly shows that the KSHV-host balance is delicately poised and any reduction in host immune competence leaves the individual at high risk of malignancy. All cases of KS worldwide, whether classic, endemic or HIV-associated, are positive for the KSHV genome and express a subset of KSHV proteins in the tumour cells1,2,5.
Primary effusion lymphoma
Primary effusion lymphoma (PEL) is a unique B cell malignancy which is seen very rarely and only in immunosuppressed patients, either KSHV-infected AIDS-patients or in KSHV-infected transplant recipients receiving high doses of immunosuppression1,2,5. It is consistently KSHV genome-positive and its development is thought to require a combination of virus infection and as yet poorly characterised cellular genetic changes. In many cases, the EBV genome is also present in the tumour cells but the significance of this is not understood.
Multicentric Castleman's Disease
Multicentric Castleman's Disease (MCD) is a B cell lymphoproliferative lesion which can be quite variable in appearance and about which little is known. It is found at low incidence in immunocompetent people, where about half of cases have the KSHV genome in tumour cells1,2,5. MCD incidence is again higher in AIDS patients and all such tumours are KSHV-genome positive.
References for Kaposi sarcoma-associated herpesvirus
- Moore, P. and Y. Chang, Kaposi sarcoma- associated herpesvirus immunoevasion and tumorigenesis: two sides of the same coin? Annu Rev Microbiol, 2003. 57: p. 609-639.
- Boshoff, C. and R. Weiss, Epidemiology and pathogenesis of Kaposi sarcoma-associated herpesvirus. Philos Trans R Soc. Lond B BiolSci, 2001. 356(1408): p. 517-534.
- Parkin, D.M., The global health burden of infection-associated cancers in the year 2002. Int J Cancer, 2006. p.3030-44
- IARC, IARC Monograph on the evaluation of carcinogenic risks to Humans Volume 67. Epstein-Barr virus and Kaposi sarcoma herpesvirus/Human herpesvirus 8. 1997. p.
- Boshoff, C. and R.A. Weiss, AIDS-related malignancies. Nat Rev Cancer, 2002. 2(5): p. 373-382.
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