A protein present in normal body tissue can prevent further growth in tumours, researchers have found.
Cancer cells must have a blood supply
A tumour can grow only if its blood supply also expands to provide it with essential nutrients.
The protein, discovered by Bristol University researchers, appears to block the growth of blood vessels past a certain size.
The researchers hope their work, published in Cancer Research, will lead to new cancer treatments.
The key protein is one of a group known as vascular endothelial growth factors (VEGF).
Most forms of VEGF stimulate blood vessel growth, including the new vessels formed as a tumour begins to develop.
However, the Bristol team have identified a form called VEGF 165b, which appears to have the opposite effect by inhibiting the growth of new blood vessels required for tumours to grow above one millimetre in size.
The researchers have also found that this form of VEGF is generally found in many normal parts of the body, including the prostate, but not in prostate cancer.
They hope it may eventually be possible to use VEGF 165b to prevent tumour growth by effectively starving it of nutrients.
The Bristol team believe that the fact that the protein is produced naturally by the body could make it more effective than other anti-cancer agents.
Many new cancer therapies are based on starving the tumour of nutrients by attacking the tumour blood supply rather than the cancer cells.
Blocking VEGF using antibodies has recently been shown to be effective in large-scale trials in colorectal cancer in the US.
New blood vessel growth is also necessary for many normal body functions.
These include the development of the embryo and, in adults, wound healing,
the development of the placenta in pregnancy and of muscles during physical
However, it is thought that adults can live healthily without blood vessel growth for extended periods of time.
This blood vessel growth is controlled by many factors, but VEGF is the most powerful factor.
Researcher Dr Dave Bates said: "Now that we have found out that this protein works in living tissues, we need to find the best way of using it in cancer, with tumour models.
"We also need to try it in models of other diseases where blood vessel growth is necessary, such as diabetes, age-related macular degeneration and arthritis."