FDA approves cell-free DNA test for colon cancer

A new blood test to detect colon cancer has been approved by the United States Food and Drug Administration (FDA).

The new test, called Shield, has been approved for use in adults who are aged 45 or older and at an average risk of colon cancer. The test is not designed to replace colonoscopies, which are the most accurate way of detecting colon cancer, but it does offer a new way to help screen people for early signs of colon cancer.

'The persistent gap in colorectal cancer screening rates shows that the existing screening options do not appeal to millions of people,' said gastroenterologist  Professor Daniel Chung, from Massachusetts General Hospital and Harvard Medical School. 'With increased screening rates and early cancer detection, many more lives can be saved.'

Cancer cells and healthy cells shed DNA into the blood, which is known as cell-free DNA (cfDNA). The Shield test is a type of 'liquid biopsy' that can detect cfDNA shed by colon cancer cells.

The approval of the test follows a recent clinical trial that assessed the accuracy of Shield in detecting colon cancer. Published in the New England Journal of Medicine, the results of the trial showed the Shield test detected 83 percent of patients with colon cancer, and about ten percent of people without cancer also received a positive result, which could be cleared up with a colonoscopy.

'People have to understand that a positive Shield test requires a colonoscopy to confirm that you have an advanced lesion or colorectal cancer, or that the results were false,' said Dr Robert Smith, senior vice president of early cancer detection science at the American Cancer Society told NBC News. 'A test like this is not complete if it’s positive and you have not had a colonoscopy.'

Colon cancer is the third most common cancer among adults in the United States, and there has been an increase in the number of people who are younger than 55 being diagnosed with colon cancer. It is thought that early detection could prevent over 90 percent of colon cancer-related deaths. Despite the importance of early diagnosis, only around 60 percent of eligible people attend their recommended colon cancer screening.