US researchers have modified blood tests that would enable them in knowing if the cancer treatment being given to a patient was working or if the disease has come back.

Tumor DNA rearrangements are identified by the test. These rearrangements are individual patient specific.

Science Translational Medicine reports that in coming years, tiny remnants of a tumor could be picked out by this genetic fingerprint.

Researchers also stated that this technology would help spotting cancer before they would be picked up by scans.

For a research, DNA for rearrangements of large chunks of genetic information was scanned from volunteer patients. These take place in cancer cells and not normal cells.

For developing the technology known as personalised analysis of rearranged ends (Pare), six sets of cancerous and normal tissue samples taken from four patients with bowel cancer and two with breast tumors were put to use.

In every sample they found four and 15 DNA rearrangements.

It was found that the test was sensitive for sensing this fingerprint DNA shed into the bloodstream by tumors. This was done using blood samples from two of the colorectal cancer patients.

After conducting tests on one patient, levels of the marker DNA dropped post surgery after the removal of the main tumor. They came back again, showing that some cancer remained.

Levels of DNA markers however fell again after chemotherapy and another round of surgery.

Study leader Dr Victor Velculescu, from Johns Hopkins Kimmel Cancer Center in Baltimore, said, "I'm quite optimistic that within five years this approach could be turned into something that's widely applicable.