text: Tumours can "seed" themselves elsewhere in the body and this process is behind 90% of cancer deaths.
  The mouse study, published in Nature, showed altering the immune system slowed the spread of skin cancers to the lungs.
  Cancer Research UK said the early work gave new insight into how tumours spread and may lead to new treatments.
  The spread of cancer - known as metastasis - is a fight between a rapidly mutating cancer and the rest of the body.
  The team at the Sanger Institute in Cambridge was trying to figure out what affected tumour spread in the body.
  Researchers created 810 sets of genetically modified lab mice to discover which sections of the DNA were involved in the body resisting a cancer's spread.
  The animals were injected with melanomas (skin cancer) and the team counted the number of tumours that formed in the lung.
  Their hunt led them to discover 23 sections of DNA, or genes, that made it either easier or harder for a cancer to spread.
  Many of them were involved in controlling the immune system.
  Targeting one gene - called Spns2 - led to a three-quarters reduction in tumours spreading to the lungs.
  "It regulated the balance of immune cells within the lung," Dr David Adams, one of the team, told the BBC News website.
  "It changes the balance of cells that play a role in killing tumour cells and those that switch off the immune system."
  The field of immunotherapy - harnessing the power of the immune system to fight cancer - has delivered dramatic results for some patients.
  A rare few with a terminal diagnosis have seen all signs of cancer disappear from their body, although the drugs still fail to work in many patients.
  Dr Adams said: "We've learnt some interesting new biology that we might be able to use - it's told us this gene is involved in tumour growth."
  Drugs that target Spns2 could produce the same cancer-slowing effect but that remains a distant prospect.
  Dr Justine Alford, from Cancer Research UK, said: "This study in mice gives a new insight into the genes that play a role in cancer spreading and may highlight a potential way to treat cancer in the future.
  "Cancer that has spread is tough to treat, so research such as this is vital in the search for ways to tackle this process."
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target: The deadly spread of cancer around the body has been cut by three-quarters in animal experiments, say scientists.