A virus that has made the human genome permanent residence for a long time can be a major cause of breast cancer, if a study presented last week at a conference in Sydney Virology, Australia is correct. Researchers say they have found a piece of the virus - which resembles a known virus that causes breast cancer in mice - in a high percentage of samples of cancerous breast tissue. If confirmed, and if a link can be established between the presence of the virus and development of cancer, the discovery could help doctors predict who is at high risk for the disease.
In recent years, scientists have identified two genes that, when mutated, can cause breast cancer, but they can not account for the great majority of cases. By the 1940s, however, virologists across a virus that causes breast, or breast tumors in mice. The mammary tumor virus of mouse called virus (MMTV) is a so-called retrovirus, a type of virus that can stick its genome into the chromosomes of infected hosts. If the land of the viral genome near one of several oncogenes of the cell, it can cause the gene to become abnormally active, leading to uncontrolled cell division and ultimately to cancer.
The discovery of MMTV sparked a hunt for a similar virus in human breast cancers. But while many researchers picked up at least indirect evidence that such viruses might be present there, a clearcut identification was hampered by the fact that the human genome carries thousands of so-called "human endogenous retroviruses elements" leftovers essentially harmless retrovirus of the ancestral man who found a permanent place in our chromosomes long ago. "This made the search for a 'HMTV' like finding a needle in a haystack," said virologist Robert Garry Tulane University in New Orleans.
Garry and his colleagues decided to take another look. They used the chain reaction highly sensitive polymerase (PCR) to search in human breast cancer samples for an MMTV gene, known as about . They chose this one because its sequence differs most from that of the comparable gene in endogenous retroviruses to ensure that any sequence they picked up was actually a linked MMTV gene. And researchers have discovered such a sequence in over 85% of the 30 samples of breast cancer. To their surprise, however, they also found in about 30% of breast tissue samples and other organs healthy people. This suggests that for Garry HMTV is an intact retrovirus that is inserted into the relatively recent human genome and is probably passed from parent to child through the germ line.
Currently, however, the finding raises more questions than answers. In 1995, for example, a team led by molecular virologist Beatriz Pogo of the School of Medicine Mount Sinai in New York also found notes of a virus like MMTV in human breast cancer tissue. But the team Pogo almost never found signs of the virus in healthy tissue or other organs - that led them to believe that HMTV was not part of the genome, but an infectious agent. And in any case, simply detecting signs of a virus in cancer tissue does not necessarily mean that it plays a causal role. One way to learn, said Alan Storey, an expert on cancer virus at the Imperial Cancer Research Fund in London, perhaps to check whether the virus-infected cells in culture become cancerous. In the meantime, Storey said, the new findings "clearly stimulate much research" in the breast-cancer virus.
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