document: Researchers at the University of Sheffield said the tumours were effectively "fertilising" the bone to help themselves grow.
  The study, in the journal Nature, said it may be possible to protect bone from a tumour's nefarious influence and consequently stop the cancer's spread.
  Cancer charities said this opened up "a whole new avenue for research".
  Around 85% of breast cancers that spread around the body end up in bone, at which point the cancer is difficult to treat and more deadly.
  The scientists, in Sheffield and the University of Copenhagen, discovered patients with secondary cancers had higher levels of an enzyme called LOX being produced by their tumours and released into the blood.
  Bone is constantly being broken down and rebuilt. But in a series of experiments on mice, the research team showed LOX was disrupting the process and leaving lesions and holes in the bone.
  Using drugs to block LOX prevented the cancer from spreading.
  Dr Alison Gartland, a reader in bone and cancer biology at the university, told the BBC News website: "We think it's a significant breakthrough in trying to prevent metastases (secondary tumours) in breast cancer.
  "The cancer cells in the primary tumour are actually fertilising the soil for the future growth of itself, LOX is changing the environment in bone to make it better to grow."
  The animal tests also showed that a set of osteoporosis drugs called bisphosphonates could prevent the spread of cancer.
  Bisphosphonates also interfere with the way bone is recycled in order to strengthen it.
  They are already given to some cancer patients, but the Sheffield team believe they could have a much larger role.
  The effect was discovered only in oestrogen-negative breast cancers. They account for around a third of cases, but are far more deadly.
  Katherine Woods, from Breast Cancer Campaign and Breakthrough Breast Cancer, said: "By unveiling the role that the protein LOX is playing, these results open up a whole new avenue for research and treatments that could stop breast cancer spreading to the bone.
  "The research also adds weight to the growing body of evidence supporting the role of bisphosphonates in stopping secondary breast cancer in its tracks.
  "The reality of living with secondary breast cancer in the bone is a stark one, which leaves many women with bone pain and fractures that need extensive surgery just when they need to be making the most of the time they have left with friends and family."
  The findings may also apply in colon cancer.
summary: Breast cancers can manipulate the structure of bone to make it easier to spread there, a study has found.