*1.2.2. Circulating cell-free nucleic acids (CFNA)*

CFNA, refers to cfDNA and extracellular RNA (exRNA - includes mRNA and miRNA), and are being widely assessed in an ongoing fashion for their potential utility as blood biomarkers for cancer diagnostics. CFNA are derived predominantly through necrosis, spontaneous or chemotherapy induced apoptosis and active cellular release [38, 39]. Given that CFNA is also present at higher levels in certain physiological conditions and clinical scenarios (reviewed in [40]), it is critical to determine if the nucleic acids released are tumour-specific in cancer patients. In this section the different types of CFNA and their potential clinical utility will be discussed.

#### *1.2.3. Cell-free DNA*

the mutational spectrum in MM, the evident shortcomings of these approaches necessitates the adoption of newer and more novel strategies to enable the more comprehensive genomic

**Figure 2.** Different sites in a MM patient may respond differentially to treatment. PET image of a MM patient receiving thalidomide therapy taken 2 months apart showing regression of disease at one site (pelvis), while tumour growth is

The utilisation of liquid biopsies continues to generate significant attention as it represents a platform that has the potential to provide rapidly evaluable and non-invasive, genomic characterisation of a patient's cancer. In simple terms, liquid biopsy refers to analyses that utilise blood or bodily fluids that contain circulating tumour cells (CTC) and/or fragments of nucleic acids or proteins that are derived from primary and/or secondary tumour sites. This material can then be interrogated to provide comprehensive information about the tumour genome and other biological characteristics of the disease. Moreover, liquid biopsies can be used to monitor the effects of therapy and may provide early evidence of recurrence or relapse of disease enabling early and informed changes in disease treatment. In this section, the two most widely studied types of liquid biopsy sources, CTC and cell-free nucleic acids (CFNA),

characterisation of the disease.

observed at another site (humerus).

76 Hematology - Latest Research and Clinical Advances

**1.2. Liquid biopsy**

will be discussed.

The presence of CFNA in body fluids was first described by Mandel and Metais in 1948 [41]. One of the earliest observations in relation to cfDNA was that patients with malignant disease had higher levels of cfDNA in their serum than normal individuals, and that patients with persistently high levels of cfDNA demonstrated a lack of treatment response [42–44]. Mutated RAS fragments and microsatellite alterations in cfDNA were later observed in cancer patients and critically these alterations were not detected in paired tissue biopsies, highlighting the concept, very early-on, that isolated tissue biopsies may not represent the optimal material for defining the tumour genome [45, 46]. The development and utilisation of NGS technologies, WGS and/ or WES of cfDNA containing tumour-derived DNA has identified mutations, tumour-derived chromosomal aberrations and gene rearrangements associated with acquired resistance to therapy without the need to perform sequential tumour biopsies [47–51]. Furthermore, it is evident that secondary mutations are more readily detectable in the plasma than via re-biopsy of primary tumours validating the utility of plasma-based analysis for the characterisation of potentially targetable oncogenes and the identification of resistance-associated mutations that are acquired during disease progression, thus informing therapeutic changes [48, 52, 53]. Available evidence would also suggest that cfDNA may be more representative of the entire tumour genome than the information derived from single BM or nodal/tumour biopsies, as emerging evidence supports the notion that a range of haematologic malignancies including MM are likely to harbour significant sub-clonal and spatial genetic heterogeneity. In MM, levels of cfDNA are significantly higher than in both normal volunteers and non-MM cancers [54, 55] and the potential utility of cfDNA in MM will be discussed below.
