Revealing the potential of liquid biopsies
Liquid biopsy is the sampling and analysis of non-solid biological material, commonly blood and urine, and it is usually associated with the diagnostic of neoplasia similar to what classical biopsies do using pieces of tissues from the suspected area. Although tumor tissue (classical biopsy) is still the gold standard source for clinical molecular analyses of solid tumors, cancer-derived material circulating in the bloodstream or excreted in the urine has become an appealing, minimally invasive alternative.
Testing for prostate-specific antigen (PSA) in blood samples, a predictor of prostate cancer, is the most classical example of a liquid biopsy. However, its specificity can be hindered by non-neoplastic prostate damage since PSA is present in both cancer and normal cells.
Nowadays, the concept “liquid biopsy” mostly refers to a test done on blood samples to look for cancer cells or for pieces of DNA from a tumor. Liquid biopsies that are tumor specific are based on the analysis of circulating tumor cells (CTCs) or circulating tumor DNA (ctDNA) shed from tumors and their metastatic sites into the blood.
· Circulating tumor DNA is tumor-derived, fragmented DNA in the bloodstream that represents faithfully the entire tumor genome. ctDNA is present at a high percentage in cancer patients with wide variability, depending on the tumor type. ctDNA allows longitudinal evaluation (blood draws taken at various time points) to monitor response to treatment, tumor progression and predict resistance and relapse. In clinics, ctDNA analysis are likely to be used complementarily to imaging for monitoring disease burden as it does not inform of the precise tumor location.
One key limitation to the use of ctDNA as a diagnostic/prognostic biomarker is the low sensitivity that means the lack of detection at diagnosis or at time of progression in some patients.
· Circulating Tumor Cells are tumor cells, detached from tumor tissue bearing the potential to seed the disease in other locations (metastasis). In contrast with other blood cells, the number of CTCs is very rare in blood which makes it very difficult to detect. These cells exist in the peripheral blood of cancer patients and detection of CTCs can help to determine the process of metastasis.
In conclusion, liquid biopsies are likely to become an additional tool for monitoring progressive genomic alterations over tumor evolution and during exposure to targeted therapies. They also might be really useful in cases where obtaining tumor tissue would have a high risk for the patient.
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