Cancer is a grave threat to human life and shakes the confidence of the most courageous of people. It is quite devastating in itself, but often what makes the life of people stricken with cancer more distressing is the treatment part. Side effects and length of treatment of cancer affect quality of life. Now, if cancer is detected early, there is a significantly higher chance of it being cured or at least the life of the patient prolonged. Recent advances in molecular genetic testing are opening up new opportunities to detect cancer early.
The use of circulating tumor DNA (ctDNA) in blood as a novel diagnostic test for the screening and surveillance of cancer is a rapidly growing area of interest, with detection of ctDNA acting as a potential surrogate for tissue biopsy. Thanks to such a blood test a doctor can identify if there is a cancer lurkingin your body at a stage when no symptoms of it are there. Such a test can also increase effectiveness of future treatment as the genetic make up of ctDNA can guide selection of correct medicine for the cancer type. And this can be done without doing an invasive test like tissue biopsy.
Liquid Biopsy – what is it?
Until now, a biopsy is considered the best and right method to diagnose cancer. It is a method where a portion or whole of tumor tissue is cut and sent to a laboratory for investigation under a microscope. Obviously, this procedure has to be invasive, often painful and requires a trained doctor to perform it. But foremost of all, the tumor has to be visible to the doctor, either to the naked eye or through the means of various imaging technologies like a CT Scan, a USG or through a scope.. For this to happen, quite often the tumor must have progressed through its course and reached a stage which cannot be termed “early”. This is the primary reason why cancer is often detected late. In a developing country like India where annual health check up or cancer screening is yet to catch up with the masses and visit to a doctor is governed by unmanageable symptoms, the battle is already half lost when a cancer is detected first.
The holy grail of cancer management is to detect it early and nip it in the bud. Of late there have been a number of clinical studies and research based on blood testing techniques such as “liquid biopsy” that would throw light on the presence of cancer early. A “Liquid Biopsy” test detects circulating tumor DNA that has been shed by a tumor into the patient’s blood. Although fragments of DNA are constantly shed into the bloodstream during normal cell death, but the levels of cell-free DNA are kept relatively low due to the rapid clearance by the liver, kidney, and spleen. In general, patients with cancer have significantly higher levels of cell-free DNA as compared to healthy individuals because tumors tend to have elevated cell turnover rates and a large number of dying cells relative to normal tissue. The median circulating plasma DNA concentration in patients with solid tumors has been noted to be three-fold higher than in healthy individuals. Furthermore, in that circulating DNA there are tell tale signs of tumor that the patient is harboring, and these signs can be picked up by a highly sensitive molecular “Liquid Biopsy” test.
Identifying DNA Fragments in Blood: How can this be useful?
There is a potential of a novel, non-invasive test that promotes early detection at a more treatable stage, reduces the necessity of tissue biopsies. Also the opportunity is there to take serial samples in order to monitor tumour genetic changes in real time. This will allow doctors to ensure that the therapy they have selected, based on a particular molecular sign of the cancer, remains relevant and observe the emergence of any resistance against therapy. For cancers that are often detected at a late stage, including lung, pancreatic, and ovarian, a high-sensitivity ctDNA assay could function as a vastly improved screening test to detect typically terminal malignancy at an earlier, potentially curable stage. So, time is not far when with a routine check up, this test can help a lot many people with high cancer risk to survive healthily for years.
So is “Liquid Biopsy” available now?
Yes and no. ‘Yes’ for a selected few tumor types where emergence of resistance against chemotherapy is common and in some cases, to monitor for recurrence of a cancer after treatment is given. ‘No’, as the test is still not conclusively validated for screening of cancers, technologies are still improving and the cost of the test is till on the higher side for routine implementation. Continued validation of circulating tumor DNA testing in large set of patients is key for establishing such tests as standard in clinical practice.