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Liquid biopsies, involving blood or other bodily fluids, can be utilized in the detection of early signs of cancer. Collection of liquid biopsy samples is quick, relatively non-invasive and painless, providing easily repeatable tool for disease diagnostics and follow-up.

When a patient has a suspicious lump or symptoms, a standard diagnostic procedure is a tissue biopsy, where a piece of tissue or a sample of cells is collected for further histopathological analysis. Doctors take a sample directly from the suspected tumour and the appearance of the cells are examined under the microscope to determine the presence of cancer and its type. Tissue biopsy sampling is an invasive procedure that involves always complication risk. If the cancer returns or if a treatment fails, repeated biopsies are needed. Sometimes tissue biopsy cannot be obtained due to inaccessibility of the tumor or other health conditions that prevent the procedure.

Effective use of current targeted cancer therapies requires regular genotyping of the tumor, since rapid genetic variation occurring in the tumor may lead to clonal heterogeneity and formation of drug resistant populations. Thus, spatially and temporally limited information acquired from a single tissue biopsy might fail to reflect its heterogeneity, and repeated biopsies are difficult to obtain [1]. Tumor can also locate in the area, from where tissue sample cannot be safely obtained and they can be scarce or unrepresentative [2]. New methods allowing a rapid, cost-effective and non-invasive identification of biomarkers at various time points during the course of disease are needed [1].

One currently developed alternative to tissue based test is so called liquid biopsy, i.e. the sampling and analysis of person´s bodily fluid. Tumour cells release circulating free DNA (cfDNA) into the blood and utilization of current highly sensitive techniques allows detection and analysis of both genetic and epigenetic aberrations characteristic for each cancer from the cfDNA. A liquid biopsy, or blood sample, can thus provide the genetic landscape of all cancerous lesions (primary and metastases) and can be used in the early diagnosis, clinical mutation detection and follow-up of treatment response, as well as in the assessment of prognosis, early detection of disease recurrence, acquired resistance and residual disease (Figure 1) [2,3].

Liquid biopsy questions.
Figure 1: Application of liquid biopsies provide answers to many key questions in cancer care. Figure modified from [4].

Utilization of liquid biopsies in the clinical work requires the harmonization of both liquid biopsy analyses methods as well as reporting of results, so that comparison of results between different laboratories is meaningful [2]. Recently, two prostate cancer researchers submitted identical patient samples to two different commercial liquid biopsy analysis providers and received results that differed substantially between two providers [5]. This confirms, that advanced clinical trials are needed before these new techniques can be transferred from research laboratories to cancer clinics.

References:

1. Heitzer E, Ulz P and Geigl JB: Circulating Tumor DNA as a Liquid Biopsy for Cancer. Clinical Chemistry, 61:1,112–123, 2015.

2. Isomursu A, Kononen J, Kuopio T: Verenkierron solunulkoinen DNA syövän merkkiaineena. Duodecim, 131:424–432, 2015.

3. Crowley E, Di Nicolantonio F, Luopakis F, Bardelli A: Liquid biopsy: monitoring cancer-genetics in the blood. Nature Reviews Clinical Oncology, 10:472-484, 2013.

4. Canadian Cancer Center website: http://www.cancer.ca/en/research-horizons/1/8/f/liquid-biopsy-for-early-cancer-detection/#ixzz58Jo7WdPk

5. Torga G, Pienta KJ. Patient-Paired Sample Congruence Between 2 Commercial Liquid Biopsy Tests. JAMA Oncology, 2017; DOI: 10.1001/jamaoncol.2017.4027.

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