Circulating tumor DNA (ctDNA) are small pieces of DNA that have almost 200 building blocks of nucleotides in length. They arise from the DNA of tumor cells. As the tumor cells rapidly divide and replaced by new cells, the dead cells get broken down, and their DNA is released into the bloodstream. Detecting ctDNA in the blood sample is what we called Liquid Biopsy. The quantity of ctDNA differs among individuals, and it also depends on the type of tumor in the body.
Tumor DNA is exactly not the same as the individual’s DNA. It may have multiple genetic mutations that lead to tumor development, and this can be efficiently analyzed by liquid biopsy. Diagnosing tumors by ctDNA can reduce the need for acquiring a sample of the tumor tissue. If the tumor is presented in the brain or lungs, it will be challenging for the doctors to obtain the sample. This technique is also used to monitor cancer patients once they have received treatment, and it is used as an indicator to check whether the treatment is successful. It is said that this test is approximately ten times more sensitive than the other previous methods.
The researchers collected samples from 105 cancer patients to test this method for finding five different cancer types with both early and late-stage disease. Fortunately, they were able to detect ctDNA at high sensitivity in patients with advanced breast cancer, melanoma, and even glioblastoma, which is very difficult to find in the blood sample. Also, they found that the ctDNA can be detected in patients with earlier cancer stage of lung or breast cancer. So, the team concluded that this method could efficiently measure the ctDNA level, thereby helping to render the patients with appropriate treatment.
Many different mutations can invariably cause a single tumor. EGFR ( Epidermal growth factor receptor) mutation in the lung cancer cell produces abnormal receptor protein, and it causes the cell to divide rapidly without any blockage. Therefore, by analyzing the genetic makeup of an individual’s tumor and targeting a set of mutations in a personalized way, this test is much more sensitive when compared to other tests.
However, this method is not efficient when the amount of ctDNA in the blood is very low. It can give a negative result even if the patient has residual cancer in their body that might relapse at any time. This technique is highly useful when there are many mutations in a cell rather than a few. Currently, this method search for hundreds and thousands of mutation in each blood samples that would reach a sensitivity of one mutant molecule in 100,000, and it could also be measured in parts per million.
In the future, this test might be more accurate in cancer patients who are more likely to relapse after treatment, and it can also lead to the development of pinprick home blood tests to monitor the patients.
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