LAUSR

The term liquid biopsy refers to the use of blood and other bodily fluids as a surrogate of tissue samples for diagnostic purposes. The rationale for using liquid biopsies instead of actual tissue samples is to avoid unnecessary invasive procedures to the patients while providing the same diagnostic information [1]. Diagnostic tests may potentially apply to any bodily fluid after proper extraction of cells, cell vesicles or nucleic acids [2]. One of the main fields of application for liquid biopsies is oncology, for the diagnosis of disease or for the identification of prognostic or predictive biomarkers [3,4]. Theoretically, any laboratory test that is performed in tissue or cytological samples can be also accomplished in liquids. Several limitations apply to the use of liquid biopsies in the clinical practice (Table 1). First of all, it should be bore in mind that in bodily fluids and therefore in any liquid biopsy the amount of diagnostic material is contaminated by normal cell components or normal nucleic acids. This is generally true also for tissue or cytological samples but in liquids the visual assessment of the enrichment of diagnostic material is impossible and it can only be estimated through characterization for cancerspecific molecular alterations. The second general consideration about liquid biopsies regards the general high dilution of diagnostic material in liquids compared to cell preparations or tissues. Therefore, in liquid biopsies we need to utilize methods that are highly sensitive. The third reflection is clinical, and concerns the short half-life of diagnostic material in liquid biopsies and their highly variable concentrations in a certain time frame. For instance, the amount of circulating free DNA or circulating tumor cells in the blood of a cancer patient may vary hour by hour and it is regulated by several cancer-related and hostrelated factors [1]. The main liquids that are managed in patients with urological malignancies are: blood and urine. The diagnostic materials found in these liquids are circulating free DNA (cfDNA) [5], circulating tumor cells (CTCs) [6] and tumor cells vesicles (exosomes) [7]. This editorial will cope with all the flaws and concerns about the use of liquid biopsies in patients with urological cancer in the pre-analytical and analytical phases of laboratory test performance.