When this happens DLC1 is no longer able to respond to biochemical signals telling a cell to die.
The scientists found that 54 out of 60 patients whose tumours were examined had elevated levels of DLC1.
A more detailed analysis revealed that five out of six samples had high levels of the modified form of DLC1.
In mice genetically engineered to over-produce DLC1, cells were found to move faster than normal, reproduce more quickly, and grow without normal cell-to-cell contacts.
The researchers traced the cancer-triggering modification to a tiny change in a chain of 19 amino acid protein building blocks in DLC1.
When his team engineered a form of DLC1 missing the modification-sensitive site, the protein no longer formed tumours.