[thedoc (OP)]

Victoria Norris  asked the Naked Scientists:
   
I notice from your website (which is excellent and very interesting by the way!) that you are a virologist and so wonder if you would be kind enough to answer a question I have had for a long time, but have never seemed to be able to find the answer to please? I recall reading various research papers and case studies over the years and have even asked some doctors, but have never been able to get the answer and as you seem to know the answer to most questions, I thought you may be able to help me!

My question relates to oncogenic viruses, eg. EBV and HPV (I note that HPV's oncogenic role in oropharyngeal cancer has been in the press recently and so is now a topical subject). Essentially, I understand that it is widely believed that cancers caused by viruses, both SCC caused by HPV and Lymphomas caused by EBV, take many years to manifest after initial infection. My question however, is does this always have to be the case? I am aware that some animal viruses are acutely transforming and so a cancer can develop within just a few months or even weeks of infection, but can viruses cause cancers in humans in timescales as short as only several months, or does the process always take years?

I am hypothesising here, but if for example the subject was pregnant at the time of infection, or taking the contraceptive pill and so mimicking pregnancy so far as hormone imbalance goes, or for the sake of argument was under huge emotional stress, eg. a close familybereavementand so immune function was impaired, do human viruses such as EBV and HPV have the ability to cause a cancer in less than a year, or is this virtually impossible/unheard of? I appreciate that as many patients do not know exactly when they were infected there is limited information on this, but I would be interested in your educated opinion.

Many Thanks!
Victoria

What do you think?

[evan_au]

Most viruses multiply rapidly and kill the cells they infect. To prevent the virus spreading, the cell may commit suicide (apoptosis), or the immune system may destroy the cell and its viral load*. A dead cell won't become cancerous; so to become cancerous, the viral infection must be non-lethal to the cell.

Retroviruses copy themselves into the host cell DNA, and then rely on the host cell copying the viral DNA to produce more viruses.

Most viruses are fairly indiscriminate about where they insert themselves:

• They may end up in a section of DNA that is continually being copied, and so start to multiply immediately
  
• Or they may end up in a part of the DNA that is never (or hardly ever) copied, lurking in the DNA for many years before breaking out.
  
• To spread as rapidly as possible, the virus normally contains a promoter segment of DNA that says "Copy Me!"
  
• If this promoter lands adjacent to genes controlling cell growth, that cell can start growing uncontrollably. This is a characteristic of cancerous cells.
  
• Viral DNA often has other segments which modify various cellular mechanisms, like disabling apoptosis, removing limitations on DNA replication or hiding the diseased cell from the immune system. These functions which aid the growth of the virus may also aid the growth of a subsequent cancer.

So an individual cell could rarely turn cancerous immediately upon infection by a virus (out of the millions affected by a viral infection). But even if this individual cell starts dividing immediately, it may take months or years to grow to a sufficient size that would cause symptoms.

Most such cancers would grow to a self-limiting size where the blood supply is inadequate, and never be noticed - until another mutation causes release of chemicals which promote blood vessel growth or spread of the cancerous cells. These cancers then become really dangerous.

See http://en.wikipedia.org/wiki/Retrovirus#Cancer
*Pregnancy & stress both affect the operation of the immune system.

[CliffordK]

There is, of course, Tasmanian Devil Facial Tumor Disease, caused by passing of malignant cells from one individual to the next.

[yellowcat]

Is a slow process. In most cases of HPV infection the immune system will remove the virus within a couple of years. In some it becomes persistent and some cells may develop precancerous changes.

This goes no further in most cases but in some people cancerous lesions will be formed.

[Matildasmith]

Yeah right..cancer is actually a slow process..it slowly deteriorates the cells and proves to be the matter of death if not treated early..every one should look out for this.