Developing a blood test for bowel cancer screening.
Dr Jeanne Tie and colleagues use the bowel cancer genome to tailor treatment to individual patients. Their work is aimed at developing a successful bowel cancer blood test that identifies whether a person has a greater risk of the cancer returning.
An oncologist and researcher, Tie combines clinical work at The Royal Melbourne Hospital and Western Health with cancer research (first at the Ludwig Institute, and now at the Walter and Eliza Hall Institute) to explore the potential of personalised medicine.
Treatment and recurrence
When Tie advises bowel cancer patients about their treatment options, the limitations of current scientific knowledge become painfully apparent.
Say the cancer was diagnosed before it spread outside the colon and the tumour was surgically removed. Statistics suggest roughly 80 per cent of these patients will survive the disease without needing six months of gruelling chemotherapy; the rest will have a recurrence. It is only the latter group who stand to benefit from the treatment, which can reduce the risk of the cancer returning. Presently Tie says she has “less than perfect” tools at her disposal to identify the patients most at risk of a recurrence.
“You do look at some features,” explains Tie, “such as how big the tumour is and so on to advise on whether they should have chemo. But they’re not very good indicators. “As a full-time clinician you’re really very busy; it’s hard to keep up with advances in cancer biology or new techniques.”
Needle in a haystack
Tie and her colleagues’ hopes lie in developing a blood test that identifies whether someone has a greater risk of the cancer returning. The test detects shards of cancer DNA in a person’s bloodstream, even when their organs appear clear on standard tests such as CT scans.
“It’s like finding a needle in a haystack because these cancer DNA are rare in the early stages of the disease,” she explains. “You need an extremely sensitive technique to differentiate cancer DNA from the normal DNA.”
Early results have been promising. In collaboration with colleagues at Baltimore’s Johns Hopkins, Tie and the institute’s Dr Peter Gibbs studied 250 patients with stage II bowel cancer (cancer that has grown through the bowel wall, but has not spread to the lymph nodes) post-surgery, testing their blood for tumour DNA. They found that cancer recurred in 80 per cent of those with snippets of cancer DNA in their blood, whereas only about 8 per cent of those without detectable cancer DNA met the same fate. Tie says another sobering finding was that a “good majority” of patients with the cancer DNA had been advised against chemotherapy, and “that really emphasised the current limitations of the system.”
What comes next?
The next step is a randomised trial of 450 patients post-surgery to gauge the usefulness of the blood test. One third will be treated routinely, getting whatever treatment their doctor advises. The other two-thirds will have the blood test, and where cancer DNA is found, chemotherapy will be offered.
Researchers also hope the test will eventually enable doctors to track in ‘real time’ the effectiveness of chemotherapy and other bowel cancer treatment for late-stage cancer sufferers.
At present, clinicians rely on CT scans to show if tumours are shrinking, though the images are often unreliable. In the longer term, Tie says, the blood test has potential as a screening tool for bowel cancer. At present, screening for the second most common fatal cancer requires a stool test.
Yet less than 50 per cent of those most at risk of developing the disease take up the option, and most of those who do, refuse a colonoscopy when the test indicates further investigation is necessary. A blood test would be an easier, less invasive alternative.
For the test to work, however, scientists must be equipped to identify all the genetic mutations for bowel cancer because, in contrast to existing cancer patients, there is no tumour tissue to compare against. “In this case it’s like looking for a needle in a haystack when you don’t even know what the needle looks like.”
Tie’s colleagues at Johns Hopkins are currently compiling a panel of genetic mutations associated with bowel cancer that has the potential to be used as bowel cancer screening blood test.