Previous research has already shown circulating tumor DNA holds promise as a biomarker for cancer, but existing methods for detecting it are not sufficiently sensitive and do not cover a diverse range of cancers. Ways to increase the sensitivity and coverage of such tests exist, but these are cumbersome and time-consuming, and need lots of steps to customize for individual patients, so they are not feasible for use in clinics.
The new approach promises to change that. It is highly sensitive and specific and should be broadly applicable to a range of cancers, say the researchers.
Their new test identified around half of patients with stage 1 lung cancer and all patients with stage 2 or higher disease. They also showed the circulation tumor DNA was highly correlated with tumor volume estimated using CT and PET scans. This suggests an approach based on the new test could monitor tumors at a fraction of the cost of present methods that rely on imaging studies.
Blood cancers like leukemia can be easier to monitor than solid tumors through ease of access to the blood. By developing a general method for monitoring circulating tumor DNA, the researchers are in effect trying to transform solid tumors into liquid tumors that can be detected and tracked more easily.
Cancer cells divide and die, even without treatment. When a cancer cell dies, the DNA in its nucleus escapes into the bloodstream. This is present in small concentrations; something like 1 in 1,000 or 10,000 bits of DNA in the blood can be from a dead cancer cell in a person with cancer.
Even in patients with advanced cancer, the vast majority of DNA circulating in their blood is from healthy, normal cells. So a test that can quickly and non-invasively monitor the tiny concentrations of cancer cell DNA would be really useful to clinicians who need to estimate the size of the tumor, how it changes over time, and monitor a patient's response to treatment.
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