Researchers believe that hepatitis virus can cause cancer
two separate studies reveal that hepatitis virus may lead to liver cancer. Randy Jirtle and his colleagues at the Duke University Medical Centre, Durham, uk , have found that hepatitis b and c viruses damage genes in liver cells, making them susceptible to cancer ( Proceedings of National Academy of Sciences , Vol 94, No 19).
Liver cells have two copies of a gene that produces a protective protein called mannose 6-phosphate/insulin-like growth factor ii receptor, or m 6 p / igf 2 r . Only one copy of the gene remains active at a given time, whereas the other is a reserve. The protein prevents liver cells from turning cancerous either by neutralising a growth factor that triggers cell division or by activating another protein that stops cancerous cell growth.
When the team examined samples of liver tissue of patients infected with hepatitis b or c , they found that cells in a large chunk of liver had only one copy of the gene. These cells apparently look healthy even if they are genetically abnormal. Once the backup gene also gets damaged, the cells start turning cancerous. Liver cancer, which is among 10 most frequently found cancers, is common among people in Southeast Asia, western Pacific, sub-Saharan Africa, and other developing countries.
In a separate study, Mei-Hwei Chang and his colleagues at the Taiwan Childhood Hepatitis Study Group, Taipei, found that a nation-wide hepatitis b vaccination during 1981-94, brought a significant decline in cases of liver cancers and death rates in children ( New England Journal of Medicine , Vol 336, No 26).
According to Arie J Zuckerman at the Royal Free Hospital of Medicine, London, liver cancer is almost 100 times as high in those who carry hepatitis virus as compared to people in developed countries who have been able to check hepatitis through effective public health measures. With nearly 80 per cent of liver cancers attributable to the microbe, hepatitis virus is the second largest human carcinogen after tobacco, he says.
The International Agency for Research on Cancer, Vienna, reports that the microbe link has widely been noticed in the third world. The two cancers -- liver and cancer of the cervix -- are responsible for more than 20 per cent of all cancers in developing countries.
Zuckerman says that a key event essential to the development of cancer is the integration of viral dna with the host cell chromosomal dna where it may either activate or suppress genes involved in normal cellular growth and proliferation.
Researchers believe that cancer-linked viruses trigger the formation of cancer by switching off tumour-suppresser genes in humans. According to Walter Eckhart, director at the Salk Institute's Cancer Centre in California, usa , such viruses cause cells to lose normal growth control and turn cancerous. At least in case of hepatitis and human papilloma virus ( hpv ), implicated in cervical cancer, there is an emerging consensus that these viruses cause cancer.
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