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Organised killers

作者:纵墩    发布时间:2019-03-07 05:12:00    

By Laura Spinney AGGRESSIVE tumours generate their own vascular networks that nourish them and help them spread to other parts of the body, say researchers in the US. This new finding could help explain why drugs designed to cut off a tumour’s external blood supply are only partially effective. Andy Maniotis of the University of Iowa in Iowa City and his colleagues made the discovery while studying skin melanoma and an unusual tumour called uveal melanoma, which affects the inside of the eye. Using electron microscopy and other techniques, they found that the most aggressive melanomas form their own vascular channels that are physically distinct from normal blood vessels. The newly discovered vascular networks lack the normal lining of endothelial cells and are arranged in an organised pattern of loops around clusters of tumour cells. Normal blood vessels are much more randomly organised. The team also detected red blood cells in the loops, which suggests that they are involved in some form of circulation (The American Journal of Pathology, vol 155, p 739). These vascular networks would explain how cells manage to survive even at the centre of a large tumour, Maniotis says. The pattern was the same when these cancers spread to other parts of a patient’s body and formed secondary tumours. “Wherever the tumour goes it makes this very peculiar patterned circulation,” says Bob Folberg, one of the researchers on Maniotis’s team. But the pattern did not show up in less invasive tumours that failed to spread quickly. So searching for the loops in tumours may allow doctors to give more accurate prognoses to people with these cancers, Folberg says. The finding could apply to other types of cancer as well, and possibly to all of them. “It’s too early to tell if it is a trademark of all aggressive tumours,” says Maniotis. “But we have preliminary data that it could be true for five different cancers.” The discovery could also explain why certain cancer treatments currently on trial do not work as well as doctors hoped. These drugs are designed to block angiogenesis—the process whereby a tumour recruits healthy tissue to form blood vessels to feed it. The new finding suggests that even if angiogenesis is halted, tumours can rely on their own vascular networks to survive. However, the hope is that it might eventually be possible to find new drugs that target the tumours’ vascular system as well, Folberg adds. Maniotis believes these strange vascular systems have not come to light before because so much cancer research has been done on animals that have been implanted with foreign, cancerous cells. This would encourage angiogenesis to dominate, because the vessel-growing process is also triggered at sites where the immune system detects infection by foreign bodies. If so, says Maniotis, scientists will have to think again about how much such animal studies tell us about cancer in people. “People are very complacent with their animal models,

 

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