Two different versions of the B-MYB gene carried by almost half of the world's population are found less often in people with cancer, the journal Nature reports.
Dr Arturo Sala of The Institute of Child Health claimed it might well reveal itself as a "key find" in cancer.
The charity Cancer Research UK claimed that more research will likely verify how it will likely help prevent the cancerous development.
More research had already shown B-MYB having a role in the development of cancer.
It has been found to be over-active in many different cancers.
The latest tests looked at just over 400 patients with either colon cancer, a tumour in the brain dubbed neuroblastoma, or chronic myeloid leukaemia.
Their version of the B-MYB gene was analysed and compared to the versions found in 230 "controls" - people with no known cancer.
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