Scientists have found that tumours can produce factors that encourage the growth of stray cancer cells lurking elsewhere around the body.
Writing in this month's edition of the journal Cell, MIT researcher Robert Weinberg and his colleagues injected mice with cells derived from human breast cancers. The mice were also injected, elsewhere in the body, with a second type of cancer cells that normally grow only very slowly. However, this time, these secondary cancers grew very fast.
The cause, the team found, was that the breast cancer cells elsewhere in the body were secreting chemical signals into the animals' bloodstreams that were speeding up the growth of the secondary tumour, although not directly. Surprisingly, the chemical signals were triggering bone marrow cells to migrate to the secondary tumours and feed them, accelerating their growth.
To understand how, the researchers looked at blood samples from the mice and found that the levels of one hormone, called osteopontin (OPN), was three times higher than normal. And when the team prevented the breast cancer cells from producing it, the bone marrow cells stopped feeding the secondary tumours, which in turn stopped growing. This suggests that the same trick could be used in humans to stall the spread of tumours.
"If metastases [cancer cells in other parts of the body] depend on stimulation by the primary tumour, interception of the signal through [for instance] neutralising antibodies might block cancer spread," says Weinberg.
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