Scientists say they have found evidence that cancer cells can go to ‘sleep’, avoiding the effects of chemotherapy, and then ‘reawaken’ years later. Researchers at the Institute of Cancer Research say this may explain why some cancers return, many years after they appear to have been cured. They analysed a patient whose leukaemia returned after 20 years in remission. The findings may help scientists to root out these dormant cancer cells, wake them up and kill them. The study, published in the journal Leukemia, found that the cancer cells which ‘woke up’ in the patient after a period of two decades were similar to a group of cancer cells that pre-dated the original bout of the disease. Blood and bone marrow samples were taken from the patient when he was diagnosed with a rare form of leukaemia at four years old and compared to samples taken when he relapsed aged 25.

In future it might be possible to speed up the growth of these pre-cancerous dormant cells so that they can be targeted and killed.

Prof Mel Greaves, The Institute of Cancer Research

Researchers identified a specific DNA mutation in cancer cells from both blood samples, in which two genes called BCR and ABL1 fuse together. They said this showed a common link between the original and the relapsing leukaemia. But they also found many new genetic changes had occurred in the cancer cells when the patient relapsed. This implies that cancer cells had become dormant, resisted chemotherapy and then ‘woke up’ after many years of rest. The cells may have survived because they were growing much more slowly than other cancer cells – and chemotherapy attacks rapidly dividing cells.

Study leader Professor Mel Greaves, director of the Centre for Evolution and Cancer at The Institute of Cancer Research in London, said the research showed that cancer cells are cunning.  “It provides striking evidence of cancer evolution in action, with cancer cells able to lie dormant to avoid treatment, and then to accumulate new mutations capable of driving a new bout of disease. “Blood stem cells regularly fluctuate between being dormant or ‘asleep’ and dividing very quickly, so it seems cancer cells are just borrowing this trick to avoid being killed by chemotherapy.”

Prof Greaves added: “In future it might be possible to speed up the growth of these pre-cancerous dormant cells so that they can be targeted and killed using chemotherapy, to reduce the risk of relapse even further.” Dr Matt Kaiser, head of research at Leukaemia and Lymphoma Research, said there were still too many children whose cancer returns. “If we can build up a picture of what causes rare cases of late relapse and how we can detect and prevent it, we may be able to deliver more true cures for this terrible disease.”

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