It is involved in many bowel cancer cases and also puts people at an increased risk of other cancers.
Five per cent of those diagnosed with bowel cancer have the HNPCC fault - of whom nearly half would have a further defect called MSH2.
The study showed that methotrexate worked particularly well in killing cells with the MSH2 genetic fault.
A clinical trial has begun at The Royal Marsden NHS Foundation Trust in London and Surrey on patients with advanced bowel cancer.
Although one of the first chemotherapies, methotrexate has not commonly been used to treat the HNPCC fault.
"Methotrexate may make an excellent treatment," the Daily Express quoted Professor Alan Ashworth, who led study, said in EMBO Molecular Medicine as saying.
Source: ANI
RAS