What began as a novel finding in pregnant women may now be a revolutionary breakthrough in oncology. In 1997 researchers in Hong Kong first discovered the presence of small chunks of the growing fetus s DNA circulating in the mother s blood. In eighteen years since its discovery, scientists have developed a way to detect and sequence this biomarker (named cell free fetal DNA or cffDNA) and have begun using it to determine several important characteristics of the developing fetus, such as its sex, its paternity and its chromosomal integrity. However, now researchers are moving it to a new realm: cancer screening.
Traditionally, the way physicians have detected cancer in patients has been through a myriad of imperfect tests such as checking for hallmark symptoms and performing biopsies and scans, but each of these has drawbacks. For example, many patients are asymptomatic and biopsies can be very invasive. Many researchers believe that this new test, which tests for circulating tumor DNA (ctDNA), the oncological equivalent of the cffDNA, may hold many benefits that the traditional screening methods simply can t offer. The testing is still in its infancy, but two studies published this month are bringing hope that this technique could be used to revolutionize the way we not only detect cancer, but also the way we monitor and treat patients.
One of the ways in which ctDNA could improve cancer treatment is through patient monitoring as they undergo a course of treatment. While it would be difficult, dangerous and hugely expensive for a patient to undergo a weekly CT scan to see if a tumor is shrinking, they can easily do a weekly blood test. A significant reduction in the levels of ctDNA could indicate that a treatment is working, while stagnant ctDNA levels would indicate that a treatment was failing. The first study, published in Annals of Oncology, looked into this possibility by monitoring ctDNA levels in patients who were undergoing treatment for metastatic colon cancer. In a study of 52 patients in Australia, the researchers found that 48 patients had detectable ctDNA in their blood. Furthermore, after a second cycle of chemotherapy, the researchers discovered a significant reduction in ctDNA levels (median 5.7-fold, p <0.001). The resultant ctDNA drops were also found to be consistent with radiological follow up tests.
The other recent study of ctDNA, published in April s Lancet Oncology, found similar results in patients with a common form of lymphoma. The researchers investigated 126 patients and found that over 80% of patients had detectable ctDNA in their blood. Furthermore, the results showed that using ctDNA to monitor for tumor recurrence was more sensitive than CT scans, as ctDNA was able to detect tumor regrowth much earlier than a scan (median 3.5 months).
Although these studies show the power of using ctDNA in fighting cancer, many obstacles still must be overcome before it can become mainstream. Many cancerous mutations are shared across tumor types so detecting ctDNA can not always provide a tumor s location. ctDNA screening also cannot say anything about prognosis or severity. Furthermore, at this stage it is cost prohibitive. Both studies used advanced high-throughput sequencing which to date is very expensive. Despite this, research into ctDNA is moving forward as a much larger study is about to begin in Australia and other smaller ones continue to be released.