Laboratory tests suggest morphine, which it is routinely prescribed to relieve pain from surgery and tumours, could in fact encourage the spread of cancer. US scientists say the opiate promotes the growth of new blood vessels which deliver tumours oxygen and nutrients. Speaking at a meeting of the American Association for Cancer Research in Boston, they also claim to have found a drug which counters this effect. Dr Patrick Singleton from the University of Chicago told the meeting of experts that in laboratory tests, morphine not only strengthened blood vessels but also appeared to make it easier for cancers to invade other tissues and spread. But he said this could be overcome by a drug – Methylnaltrexone or MNTX – developed in the 1980s to prevent morphine-related constipation but only recently approved in the US. It appears to work without interfering with the pain-relieving properties of the opiate. Cancer Research UK, however, said more tests were needed before any changes in treatment.