Circulatingtumordna (Ctdna) in Prostate Cancer: Current Insights and New Perspectives

Circulatingtumordna (Ctdna) in Prostate Cancer: Current In-
sights and New Perspectives
Conteduca V*
Department of Medical Oncology, Istituto Scientifico Romagnolo per lo Studio e la Cura dei Tumori (IRST) IRCCS, Italy
Volume 1 Issue 1 - 2018
Received Date: 20 May 2018
Accepted Date: 05 June 2018
Published Date: 07 June 2018
1. Abstract
Prostate Cancer (PC) is the common tumor in men, which represents one of leading
cause of cancer death throughout the world. Most patients were diagnosed too late for cura-
tive treatment. So, it is necessary to develop a minimal invasive method to identify novel bio-
markers. Currently, plasma DNA has attracted increasing attention as a potential tumor marker.
However, to date its origin remains still unknown. Recent findings showed that a fraction of the
plasma DNA is derived from the tumor itself, and genetic and epigenetic alterations are regu-
larly detected in PC patients. Many studies have evidenced an association among the plasma
DNA analysis, Gleason score, tumor stage, lymph node status, clinical progression, develop-
ment of metastasis, and clinical outcome, concluding that plasma DNA levels could serve as
a viable tool for diagnostic and prognostic information in prostate tumor. In addition, several
genetic and epigenetic changes, identified by recent genotyping and sequencing technologies,
such as copy number variation, point mutation, loss of heterozygosity, microsatellite instabil-
ity, and gene methylation were correlated with treatment response and resistance mechanisms.
Here, we reviewed the evidence of plasma DNA in PC and consider current and possible future
applications in patient management.
3. Introduction
Prostate Cancer (PC) is one of the three most common
cancer type for the estimated new cancer cases and deaths, respec-
tively, among men in worldwide [1]. PC is highly heterogeneous in
terms of the clinical behavior and molecular pathogenesis. There
is a plethora of clinical situations between indolent and aggressive
tumors and within the same setting, particularly in the Castration-
Resistant Prostate Cancer (CRPC). In addition, tumors with the
same histopathologic grade are often biologically heterogeneous
with different outcome. The remarkable variation in PC clinical
behaviour reflects the broad landscape of molecular alterations
among various prostate tumors and within the same tumor at dif-
ferent stages of disease progression [2-4].
On the basis of wide heterogeneity of prostate tumor, more pre-
cise biomarkers are needed to help accurately the identification
of indolent or aggressive PC, a better knowledge of the genetic
Clinics of Oncology
Citation: Vincenza Conteduca. Circulatingtumordna (Ctdna) in Prostate Cancer: Current Insights and New
Perspectives Clinics of Oncology. 2018; 1(1): 1-12
united Prime Publications: http://unitedprimepub.com
mechanisms of tumor progression and the optimization of PC
management.
Over the years, the use of serum Prostate-Specific Antigen (PSA),
the only routine test approved for the PC screening, detection and
treatment response has become a highly debated question for the
lack of specificity leading often to the over detection and over-
treatment of prostate tumors [5-8]. Consequently, the identifica-
tion of novel biomarkers is one of the most important issue for PC
management and further studies for their validation and intro-
duction into clinical practice are warranted the identification of
novel biomarkers is one of the most important issue for PC man-
agement and further studies for their validation and introduction
into clinical practice are warranted [9,10].
With advances in genotyping and sequencing technologies, the
development of non-invasive methods to detect and monitor tu-
mors continues to be a major challenge in oncology. New molecu-
2. Keywords
Plasma DNA; Prostate cancer; Bio-
marker; PCR; Sequencing
*Corresponding Author (s): Vincenza Conteduca, Department of Medical Oncology,
Istituto Scientifico Romagnolo per lo Studio e la Cura dei Tumori (IRST) IRCCS, Italy,
Tel: +39-0543-739100; Fax: +39-0543-739151; Email: vincenza.conteduca@irst.emr.it
Research article

lar biomarkers are based on a combination of multiple genomic or
proteomic biomarkers.
This review will focus on the role of circulating tumor DNA (ctD-
NA) as recent discovery in the “liquid biopsy” field of many solid
tumors, including PC [11-14]. In recent years, measurement of
ctDNA might become as efficient complementary tools to guide
future therapeutic directions and improve the outcome of PC pa-
tients.
4. Biology of Circulating Cell Free DNA
Circulating free DNA (cfDNA) has been detected in
the plasma of cancer patients as well as in that of healthy con-
trols. However, circulating tumor DNA (ctDNA) is approximately
three-four times the cfDNA amount of healthy controls, even if
it often represents only a small fraction (less than 3.0%) of total
circulating DNA [13,15,16]. Different potential mechanisms may
be involved in the cfDNA release into the circulation and could
include both cancer and healthy cells. Certainly, low levels of
cfDNA in healthy individuals are due to the activity of infiltrating
phagocytes that, however, under specific conditions (e.g., tumor,
inflammation, etc.), might not clear apoptotic and necrotic debris
properly [17].
The apoptosis and necrosis of tumor cells represent the most prob-
able mechanisms for the ctDNA release into the bloodstream [13].
In addition, living cancer cells could actively release DNA into the
circulation because of possible oncogenic property to affect the
transformation of susceptible cells leading to metastasis forma-
tion [17,18]. ctDNA might also be released by Circulating Tumor
Cells (CTCs) shed by tumor [13,16]. However, a single human cell
contains 6 pg of DNA with an average of 17 ng of DNA per ml
of plasma in advanced tumors. Therefore, there is a discrepancy
between the number of CTCs and the amount of ctDNA. If CTCs
were the main source of ctDNA, there would be more than 2,000
cells per ml of plasma; indeed, there are, on average, less than 10
CTCs per 7.5 ml blood [19-21]. In conclusion, at correlation be-
tween ctDNA and CTCs might exist but they represent separate
entities and, in some cases, ctDNA could be identified also in the
absence of detectable CTCs [11,22,23].
Other host elements that might contribute to the source of ctDNA
are plasma nucleases (e.g., DNase 1) that could have a decreased
DNase activity in the plasma of cancer patients [24,25]. Moreover,
tumor microenvironment could have a role for ctDNA release be-
cause of the induction of apoptosis by pro-apoptotic cytokines by
inflammatory cells or cancer cells. In fact, some studies showed
higher level of ctDNA not only in PC, but also in patients affected
by Benign Prostatic Hyperplasia (BPH) compared with healthy
controls [26,27].
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These data supported the theory that a large proportion of cfDNA
was derived from noncancerous cells because of the induction of
apoptosis by proapoptotic cytokines released from prostate cancer
cells.
In addition, the host factors for ctDNA clearance [13], other fac-
tors influencing ctDNA amount are related to tumor (size, stage
and, probably, type of tumor). In general, major burden tumor
and metastatic disease are characterized by increased ctDNA lev-
els [14,28].
The analyses of DNA fragmentation showed that apoptotic or ne-
crotic pattern seems to be different in distinct types of cancer. In
general, fragmentation of cell-free DNA is higher following apop-
tosis than following necrosis or phagocytosis [28]. In fact, ctDNA
fragments longer than 10,000 bp originate usually from necrotic
cells, whereas DNA fragments shorter than 1000 bp, particularly
of 180 bp or multiples of this size, are observed in apoptotic cells
[12,28]. A detailed analysis of the size of the ctDNA fragments
could allow discerning the source of circulating nucleic acid in n
various cancer entities. Specifically, necrotic pattern seems to be
predominant in patients with breast and gynaecological [29,30],
colon [31], testicular [32], and head and neck [29] cancer patients
because necrotic breakdown leads to greater DNA integrity. On
the other hand, the presence of mainly short DNA fragment in cir-
culation of patients with bladder cancer [33] and PC [34] argues
for apoptotic pattern of ctDNA release.
The combined analyses of ctDNA with CTCs or Disseminated Tu-
mor Cells (DTCs) in bone marrow suggest that ctDNA may be
derived not only from the primary tumor but also from micro-
metastatic cells. Consequently, some studies showed that the pres-
ence of ctDNA may be correlated to the detection of DTCs in bone
marrow of PC patients [13,35,36].
5. Methods for ctDNA Analysis
Recent advances in the sensitivity and accuracy of DNA
analysis are leading to genotype ctDNA for genomic aberrations,
including somatic single nucleotide polymorphisms, chromosom-
al rearrangements and epigenetic alterations [37-41].
Preanalytical factors involved in sample collection (i.e., the pre-
ferred use of plasma compared to serum, the addition of anti-
coagulant EDTA in collection tube, proper blood centrifugation
after blood collection, etc.) and highly sensitive techniques are
mandatory for the ctDNA analysis because of the small fraction of
ctDNA present within normal cfDNA [42].
Currently, many discoveries in genomics technologies are provid-
ing novel challenges for the analysis of ctDNA. In general, it is
volume 1 Issue 1-2018 Research article

possible to subdivide the approaches for ctDNA analysis into three
groups: a) Polymerase Chain Reaction (PCR) based methods, b)
targeted deep sequencing, and c) whole sequencing [43]. The PCR
based approaches are usually used for the evaluation of a low num-
ber of loci, even digital PCR is considered as a sensitive analysis
tool for the identification of mutations at low allele fraction [44].
Methods involving the use of digital PCR include droplet-based
systems [45,46], microfluidic devices [22,47], and the use of Beads,
Emulsions, Amplification and Magnetics (BEAMing) [48,49]. An
example of the utility of PCR based approaches for ctDNA analysis
is showed by a work evaluating the prognostic utility of circulating
plasma testing in 85 patients with different advanced solid tumors.
Specifically, the presence of NRAS, PIK3CA and AKT1 was dem-
onstrated in 3 of 11 (27.3%) circulating DNA specimens of CRPC
patients and PIK3CA and AKT1 were found in the corresponding
formalin-fixed paraffin-embedded tumor tissue pointing up that
circulating plasma DNA in advanced cancer patients is largely de-
rived from tumor [21].
Next Generation Sequencing (NSG) methods are characterized
by more complete detection of mutations across larger genomic
regions. They revolutionized the field of genomics, allowing rapid
and cost-effective generation of genome-scale sequence data with
excellent resolution and accuracy.
Targeted deep sequencing using PCR-based (e.g. TAm-Seq
[22,50,51], Safe-Seq [52], Ion AmpliSeq™ [4,53] or capture-based
(e.g. CAPP-seq [54]) approaches have been used to sequence spec-
ified genomic regions in plasma DNA. The utility of targeted deep
sequencing in PC is showed in a recent study describing the clonal
architectural heterogeneity at different stages of disease progres-
sion.This work evaluated genomic aberrations by sequencing se-
rial plasma and tumor samples from 16 ERG-positive PC patients
treated with abiraterone, achieving high coverage with lower in-
put DNA (approximately 6 ng) and allowing applicability across a
larger range of patients, including those with lower tumor burden.
In addition, combining targeted deep sequencing and read based
clonality computations provided timely non-invasive biomarkers
for CRPC clinical management [4].
Whole-genome analysis of plasma DNA permits the complete
characterization of mutation profiles, without focusing on pre-
defined mutations [51]. Among these methods, there is personal-
ized analysis of rearrangement ends, which allows to identify spe-
cific somatic rearrangements in human tumors and, subsequently,
to design of PCR-based assays to detect these alterations in plasma
DNA, using these alterations for development of tumor biomark-
ers [39,40]. Some studies have used whole genome sequencing to
detect directly somatic chromosomal alterations and copy num-
ber aberrations in ctDNA genome-wide [38,40]. The first whole-
genome sequencing analysis from plasma DNA of 13 patients with
prostate cancer revealed multiple copy number aberrations and
chromosomal aberrations [55].
With continued developments in the sensitivity of genomic ap-
proaches, NGS techniques will be increasingly able in ctDNA
analysis for future management of many tumors, including PC
at different disease stages, advancing precision medicine for PC
through genomics clinical applications.
6. Application of Circulating DNA in Prostate Cancer
6.1. Early detection: The 2012 recommendations of the United
States Preventive Services Task Force [8] and the National Com-
prehensive Cancer Network (NCCN) Guidelines for Prostate
Cancer Early Detection Panel [56] show a decreased mortality in
populations screened with PSA, stressing benefits from PC screen-
ing and early detection. However, many improvements are being
made to enhance powerful tests that maximize early diagnosis
of aggressive, but often curable disease, whereas diminishing the
identification and treatment of indolent disease. cfDNA could be
useful to discriminate between patients with PC and no malig-
nant prostate disease. Many studies have explorated the utility of
cfDNA as a marker of tumor dynamics in addition to conventional
PSA or imaging techniques. However, the results have been often
conflicting according to different cfDNA isolation and detection
methods and various clinical setting.
Quantitative and qualitative alterations between patients with
diagnosis of PC and nonmalignant lesions, including Prostatic
Intraepithelial Neoplasia (PIN) and Benign Prostate Hyperplasia
(BPH), have evaluated the role of cfDNA in screening and early
detection. Many studies have demonstrated that higher cfDNA
levels in PC patients are able to identify patients with malignant
disease; however, contrasting results have emerged from other
studies making the use of cfDNA a topic of much debate in oncol-
ogy [25-27,36,57-62] (Table 1).
The first study [27], published in 2004, did not demonstrate signif-
icant differences between patients with clinically localized PC and
BPH; on the contrary, it showed a significant increase of plasma
DNA levels in patients with metastatic PC compared to controls.
Another study failed to detect significant differences between pa-
tients with PC and benign prostate diseases [26]. Seventy-eight PC
patients had a significantly higher level of DNA compared with
the control group, but they had significantly lower level of DNA
than 74 patients with benign diseases (P = 0.02).Consequently,
this study suggested that elevated cfDNA levels could not be used
as a new non-invasive approach for PC early detection. These data
have been confirmed in a subsequent study [25] showing a ma-
jor cfDNA concentration in BPH patients than PC patients and,
a lower cfDNA in healthy donors compared to PC patients (P <
0.01), most likely due to the reduced DNase activity in the blood
plasma of PC patients
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The failure to distinguish BPH and localized PC may have differ-
ent causes, including the use of a less sensitive fluorometric assay,
or the presence of other diseases within the prostate gland, such as
prostatitis, which may be elevating the cell-free DNA level perhaps
to a greater degree than that of PC.
Recent studies employed a real-time PCR and demonstrated sig-
nificant higher DNA levels in PC then in BPH patients and healthy
donors with good values of sensitivity and specificity (more than
UTILITY OF QUANTITATIVE ALTERATIONS
YES NO
Study
PC
(number
setting)
Control
(number,
setting)
Source,
Method
Results Study
PC
(number,
setting)
Control
(number,
setting)
Method Results
Allen et al. [57]
27 (12 high
grade PIN,
15 PC)
10 (BPH) Plasma, PCR
S: 85%
Jung et al. [14]
91 (32
pNoMo, 30
pN1M0 29
M1)
93 (30
female
controls,
29 HD, 34
BPH)
Plasma,
Flurome-
tric assay
S:n.s.
Sp: 73% Sp:n.s.
AUC:n.r. AUC:n.s.
P:0.04
(PIN vs
HD);
P: 0.140*
P:0.01 (PC
vs HD)

Papadopoulou et
al. [58]
12 13 Plasma, PCR
S: 58%
Boddy et al.
[26]
78
99 (74
benign, 15
low-risk
benign, 10
HD)
Plasma,
PCR
S: n.s.
Sp: 92% Sp: n.s.
AUC:
0.708
AUC: n.s.
P: n.r.
P (benign
vs. PC):
0.0001;

P (PBH vs.
PC): 0.02
Chun et al. [59]
142 (local-
ized PC)
19 (BPH)
Plasma,
Spectropho-
tometry
S: n.r.
Cherepanova
et al. [25]
5
52 (22
BPH, 30
HD)
Flurome-
tric assay
S: n.r.
Sp: n.r. Sp: n.r.
AUC: n.r. AUC: n.r
P: 0.032 P: n.s. **
Altimari et al. [60] 64 45 (HD) Plasma, PCR
S: 80%

Sp: 82%
AUC:
0.881
P <0.001
Ellinger et al.
[33,34]
173
53 (42
BPH, 11
HD)
Serum, PCR
S: 88%

Sp: 64%
AUC:
0.824
P <0.001
Schwarzenbach
et al. [36]
69 (PC M1) 12 (PC M0) Plasma, PCR
S: n.r.

Sp: n.r.
AUC: n.r
P: 0.03
Wroclawsky et
al. [37]
133 33
Plasma,
Spectropho-
tometry
S: 66.2%

Sp: 87.9%
AUC:
0.824
P<0.05
Feng et al. [61] 96 112 (BPH) Plasma, PCR
S: 73.2%

Sp: 72.7%
AUC:
0.864
P<0.001
Table 1. Role of circulating free DNA levels for early detection of prostate cancer.
58% and 64%, respectively) [34,36,57,58,60,61]. Among PCR-
based studies, the largest one [34] included 216 patients, whose
173 with PC and 53 controls (11 healthy individuals and 42 with
BPH) and had by a sensitivity of 88% and a specificity of 64%. In
this study, the analysis of PTGS2 DNA fragment, that biochemi-
cally characterizes apoptosis, showed DNA fragment levels in se-
rum of patients with PC signiﬁcantly increased in comparison to
BPH patients and healthy individuals (both P<0.0001). Another
important study [60], quantifying by real-time PCR assessment

cfDNA in plasma samples from 64 patients with localized PC and
45 healthy males, showed a better discrimination between PC and
healthy subjects with a sensitivity of 80% and a specificity of 82%.
It concluded that ctDNA quantification could be a candidate bio-
marker for early diagnosis correlating with pathologic tumor stage.
A prospective study [59] also detected increased DNA levels in 161
PC patients using spectrophotometry. The median plasma concen-
tration of cfDNA was 267 ng/mL in men with BPH and 709 ng/mL
in men with PC. Uni-and multivariate analyses (after controlling
for age, total PSA, free/total PSA, prostate volume) suggested that
cfDNA was highly accurate and informative predictor (P=0.032
and predictive accuracy 0.643) for the presence of PC on needle
biopsy. A recent study [62] of 133 patients affected by PC and 33
controls used also spectrophotometry that confirmed cfDNA as a
potential tool for PC diagnosis with sensitivity of 66.2% and speci-
ficity of 87.9% and the additional role of cfDNA during follow-up
of PC patients.
For the discrimination between PC and benign conditions, the
identification of genetic and epigenetic alterations in cfDNA may
be also an interesting tool for molecular screening of PC patients.
The presence of allelic imbalance, including loss of heterozygos-
ity and microsatellite DNA, has been investigated on circulat-
ing DNA of PC patients in PCR-based studies, characterized by
a sensitivity ranging from 34% to 57% and specificity from 70%
to 100% [35,36,63-65]. Diagnostic information derives also from
cell-free DNA hypermethylation, especially the hypermethylation
of GSTP1 (Glutathione S-Transferase 1 Pi gene), a detoxifying
enzyme present in about 30% of PC patients. Many studies us in
gmethylation-specific PCR tests, characterized by a high speci-
ficity nearly 100% for the presence of prostatic neoplasia, but by
a variable sensitivity ranging from 11% to 100%, suggested that
measurement of GSTP1 promoter methylation in plasma, serum,
or other samples may complement PSA screening and early detec-
tion for PC diagnosis [58,60,64,66-75].
Finally, some studies [34,76] showed also the utility of the DNA
Integrity Assay (DIA) as a plasma-based screening tool for the PC
detection.In 2006, Hanley et al. [76]evaluatedblood samples pa-
tients with biopsy-proven PC prior to prostatectomy (n = 123). He
studied three control groups including young men with no his-
tory of cancer (group 1, n = 20); cancer-free post-prostatectomy
patients (group 2, n = 25), and patients with a negative prostate
biopsy (group 3, n = 22). A baseline cutoff was used for individual
DNA fragment lengths to fix a DIA score for each patient sample.
PC patients (86 of 123; 69.9%) had a strongly positive DIA score.
The DIA results from control groups 1, 2, and 3 showed specifici-
ties of 90%, 92%, and 68.2%, respectively. So this study concluded
that DIA could detect approximately 70% of PC patients with a
specificity of 68.2% to 92%, a range similar to that currently ac-
cepted for PSA (60-70%).
6.2. Prognostic role: Recent evidences highlighted the clinical
importance of increased levels of cfDNA and presence of genetic
and epigenetic alterations as an adverse prognostic marker in PC
patients. In 2004, Jung et al. [27] published the first study that em-
phasized cfDNA concentration as a survival predictor in PC pa-
tients. It showed survival curves of 91 PC patients (stage pN0M0,
n=32; stage pN1M0, n=30; stage M1, n=29) according to the plas-
matic concentrations of DNA, total PSA, and osteoprotegerin as a
marker for bone metastases. The association between plasma DNA
and the survival was similarly strong as with PSA but only in pa-
tients with distant metastases.
Lately, a retrospective study of 59 taxane-based chemotherapy
treated PC men [77] showed the role of cfDNA level as a prognos-
tic marker according to PSA response and survival. Patients with a
PSA decline of more than 80 % had a lower cfDNA concentration
compared to patients with the least PSA decline of less than 30%.
In addition, cfDNA level was associated with a significantly longer
survival rate (31 months in patients with cfDNA levels of less than
55ng/μl compared to 17 months in patients with higher concen-
trations) (p=0.03). Another recent work [78] aimed to clinically
qualify baseline and on-treatment cfDNA levels as biomarkers of
patient outcome treated with taxane chemotherapy. The authors
analyzed blood samples prospectively collected from 571 mCRPC
patients participating in two phase III clinical trials, FIRSTANA
(NCT01308567) and PROSELICA (NCT01308580). They iden-
tified that baseline log10 cfDNA concentration correlated with
shorter radiographic PFS (HR 1.54; 95% CI 1.15–2.08; P=0.004),
and shorter OS on taxane therapy (HR 1.53; 95% CI1.18–1.97;
P=0.001), and cfDNA concentration before starting docetaxel or
cabazitaxel was an independent prognostic variable on multivari-
able analyses for PFS and OS in both first- and second-line che-
motherapy settings. Patients with a PSA response experienced a
decline in log10 cfDNA levels during the first four cycles of treat-
ment.
Survival analysis from a phase I exploratory cohort of 75 men
with CRPC and a phase II independent validation cohort of 51
CRPC men [74] demonstrated that detection of plasma methyl-
ated GSTP1 in CRPC patients was associated with a shorter OS
(HR 4.2, 95% CI 2.1-8.2; P<0.0001). The 2-year survival for men
with no detectable plasma mGSTP1 was 71% compared with 23%
for men with detectable plasma methylated GSTP1 levels.
The prognostic value of cfDNA and circulating DNA fragments
of apoptotic origin (i.e., PTGS2 DNA fragment that biochemically
characterizes apoptosis) has also been showed in PC men as pre-
dictor of PSA recurrence after radical prostatectomy [34,79] and of
biochemical recurrence free survival during follow-up in plasma

samples of 133 PC patients collected prospectively every 3 months
for 2 years (P = 0.048) [62].
In addition, cell-free DNA hypermethylation of GSTP1, Ras as-
sociation [RalGDS/AF-6] domain family member 1 (RASSF1A)
and retinoic acid receptor β, variant 2 (RARB2) was also corre-
lated with the Gleason score, tumor stage, extent of metastasis
[64,69,74].
Currently, the identification of genetic aberrations in cfDNA has
emerged as a promising prognostic biomarker. Recent studies
[4,80-86] demonstrated a significant correlation between aberra-
tions (copy number variations and point somatic mutations) of
Androgen Receptor (AR) detected in blood and treatment out-
come in CRPC patients treated with second generation hormonal
drugs, abiraterone or enzalutamide. One of the most recent bio-
markers studies [83] was aimed to clinically qualify AR status
measurement in plasma DNA from 265 CRPC patients (191 in
the primary cohort and 94 in the secondary cohort), using an op-
timized multiplex droplet digital PCR (ddPCR) assay in pre- and
post-chemotherapy CRPC.AR gain was observed in 10 (14%) che-
motherapy-naïve and 33 (34%) post-docetaxel patients and was
associated with a worse OS (HR 3.98; 95% CI, 1.74-9.10; P<0.001
and HR 3.81; 95% CI, 2.28-6.37; P<0.001 respectively), PFS (HR,
2.18; 95% CI, 1.08-4.39; P = .03, and HR, 1.95; 95% CI 1.23-3.11;
P=0.01, respectively) and rate of PSA decline ≥50% (Odds ratio
(OR) 4.7; 95% CI, 1.17-19.17; P=0.035 and OR 5.0; 95% CI 1.70-
14.91; P=0.003 respectively). AR mutations (2105T>A (p.L702H)
and 2632A>G (p.T878A)) were observed in 8 (11%) post-docetax-
el but no chemotherapy-naïve abiraterone-treated patients and
were also associated with worse OS (HR 3.26; 95% CI, 1.47-not
reached; P=0.004). These data were confirmed in the secondary
cohort of the study and plasma AR resulted an independent pre-
dictor of outcome on multivariate analyses in both cohorts.
6.3. Predictive role and treatment resistance: Treatment resis-
tance may develop mainly for an incessant evolving spectrum of
genetic and epigenetic alterations within the tumor under the se-
lective pressure of therapy. The analysis of ctDNAcould integrate
invasive biopsy approaches to evaluate noninvasively from plasma
DNAgenomic alterations related to acquired drug resistance in
advanced cancers [51]. Beyond the prognostic role, recent stud-
ies [4,79,83] have demonstrated the association between clinical,
biochemical and radiographic response and genomic aberrations,
especially involving AR, in ctDNA of CRPC patients treated with
novel hormonal therapies, as abiraterone and enzalutamide [4,80-
86]. Carreira et al. [4] sequenced serial plasma and tumor samples
from 16 ERG-positive lethal PC patients and identified genomic
lesions, including common tumor deletions, AR copy number
gain, functionally active AR mutations. This study demonstrated
a temporal association between clinical progression and emer-
gence of AR mutations activated by glucocorticoids in about
20% of patients progressing on abiraterone and prednisolone
or dexamethasone. A subsequently study [80] of 53 consecu-
tive CRPC patients treated with abiraterone after chemother-
apy showed that AR or CYP17A1 amplification in cfDNA led
to early progression disease that occurred within 4 months of
the start of abiraterone treatment. So, the authors concluded
that CNVs of AR and CYP17A1 genes were predictive of early
resistance to therapy. Azad et al. [84] confirmed the utility of
cfDNA to identify therapeutic resistance to novel hormonal
drugs. They used array Comparative Genomic Hybridization
(aCGH) for chromosome copy number analysis and NGS of
exon 8 of the AR in cfDNA samples from 62 metastatic CRPC
patients stopping abiraterone (n=29), enzalutamide (n=19) or
other agents (n=14) due to disease progression. The results
from aCGH showed that AR amplification was significantly
more frequent in patients progressing on enzalutamide than
on abiraterone or other agents (53% vs. 17% vs. 21%, P=0.02).
Missense AR exon 8 mutations were detected in 11/62 patients
(18%), including enzalutamide- and abiraterone-resistant pa-
tients.
In addition, a recent prospective study [74] showed the asso-
ciations between detectable plasma mGSTP1 prior to chemo-
therapy and no response to chemotherapy (docetaxel or mito-
xantrone) and so epigenetic alteration could be also a potential
surrogate therapeutic efficacy marker for chemotherapy.
6.4. Role in follow-up: In this era of survival prolonging drugs
in the treatment of PC patients, the identification of noninva-
sive biomarkers for monitoring patients during follow-up is
essential. Wroclawsky et al. [62] showed a significant shorter
biochemical recurrence free survival for patients with at least
one value of cfDNA greater than140 ng/mL during a mean fol-
low-up of 13.5 months (P=0.048).
The utility of cfDNA in follow-up of PC patients has emerged
also from the relation between the measurement of cfDNA and
radiographic imaging. Kwee et al. [87] explored cfDNA content
in relation to fluorine-18 Fluorocholine (FCH) positron emis-
sion tomography/computed tomography (PET/CT) in 8 CRPC
patients receiving docetaxel-based chemotherapy. Serial cfDNA
samples were assessed by microfluidic electrophoresis, quanti-
fied by real-time PCR, and compared with results from FCH
PET/CT scans, used for whole-body measurement of tumor
activity results. Promoter methylation of two PC-associated
genes, GSTP1 and RARB2, was evaluated by methylation-spe-
cific PCR. Plasma cfDNA concentrations increased significant-
ly after one and three treatment cycles, respectively (P=0.001).

GSTP1 and/or RARB2 promoter methylation was identified in
all pretreatment samples. The appearance of large (200 bp-10.4
kb) cfDNA fragments and loss of methylation at GSTP1 and/or
RARB were observed after treatment. Tumor activity on PET/CT
correlated significantly with cfDNA levels and PET/CT tumor re-
sponse had significantly lower before therapy cfDNA levels than
those who did not (P=0.03). These preliminary data exploratory
examinated the translational significance of cfDNA as therapeutic
response marker, but larger studied are warranted.
7. Comparison between Circulating DNA in Plasma and
in Other Body Fluids
Like blood, urine and semen represent a source of cfDNA which
can be gained in a more noninvasive manner and could therefore
be useful as an easy substrate for biomarker measurement in PC
patients. In 2013, the pilot study [88] investigating the potential
role of urinary cfDNA in early PC diagnosis. The authors analyzed
urinary cfDNA fragments longer than 250 bp in three regions fre-
quently amplified in solid tumors, including PC: c-Myc (8q24.21,
HER2 (17q12.1), and BCAS1 (20q13.2) and concluded that urine
DNA integrity could distinguishing between PC patients and
healthy individuals with an accuracy of about 80%, similar to that
observed previously for bladder cancer [89,90]. However, this
finding of longer cfDNA fragments in urine of PC patients was
apparently in contrast to the presence of short DNA fragments in
blood, as shown in previous work [34]. Conversely, the same pro-
file of GSTP1 gene promoter methylation has been demonstrated
in the pool of circulating and extracellular DNA from the blood
and urine of PC patients. This profile differs from those charac-
teristic of healthy donors and BPH patients, confirming that the
quantification of cfDNA in different body fluids from blood, such
as urine and ejaculates, could represent a diagnostic tool charac-
terized by the ability to detect PC and lower the rate of unneces-
sary biopsies [66,91].
7.1. Comparison between cfDNA and other circulating bio-
markers: Over cfDNA, other cell-free nucleic acids, including
mRNA and microRNA (miRNA) are released and circulate in the
blood of PC patients, probably from the same apoptotic or necrot-
ic cells originating cfDNA. Changes in the levels of other circu-
lating nucleic acids have been associated also with tumor burden
and malignant progression. RNA released into the blood stream is
more stable in spite of the increased amounts of circulating RNas-
es. Consequently, RNA may be protected from degradation by its
packaging into exosomes, such as microparticles, microvesiclesor
multivesicles, which are shed from cellular surfaces into the cir-
culation. For the detection and identification of RNA microarray
technologies or reverse transcription quantitative real-time PCR
are used [13] (Figure1).
Figure 1. Current and future potential applications of circulating DNA in pros-
tate cancer patients.
Prostate-derived exosomes (also called prostatosome) are endo-
some-derived vesicles with a diameter between 50 and 150 nm
that contain cytoplasmic content (proteins and RNAs) encapsu-
lated by a cholesterol rich phospholipid membrane. It is possible
to detect exosomes in blood, urine and semen [92]. Some studies
suggested the diagnostic and prognostic role of prostatosomes, re-
vealing a higher number of exosomes in blood of PC patient com-
pared to men with no disease and correlating exosome number
with Gleason score [93,94]. In addition, recent studies revealed
that the detection of a splice variant of AR (AR-V7) in plasma-
derived exosomal RNA strongly predicted resistance to hormonal
therapy in metastatic CRPC patients, making exosomes a poten-
tial source of clinically relevant biomarkers [94].
Among circulating biomarkers of PC, one area of expanding in-
vestigation is CTCs, rare cells that are shed from primary and
metastatic tumor deposits into the peripheral circulation [95].
Enumeration of CTCs before and after therapy has shown that
CTC burden correlates with outcome in CRPC patients [96-98].
Moreover, studies have demonstrated the potential of molecular
analysis of CTCs in monitoring and predicting response to thera-
py in patients [99].
Both CTCs and ctDNA offer snapshots of genomic alterations in
primary tumors and metastases at various stages during the course
of disease. However, there are yet some limits for the use of CTC
and ctDNA as liquid biopsies. Because CTCs are very rare cells,
capturing them depends on rather sophisticated equipment, while
plasma DNA is easily obtained, even tumor DNA fragments are
diluted with various amounts of DNA from normal cells, which
may hinder analysis [100]. Despite these limitations, combining
both ctDNA and CTC analyses as a blood biomarker panel results
in a higher diagnostic accuracy compared to the use of a single

marker. Concerning the heterogeneity of the disease, the future
prospect will have to be focused on the combination of differ-
ent circulating biomarkers to improve PC management.
Recently, it has emerged that detection of AR-V7 in CTCs
may represent one such treatments election marker in men
with metastatic CRPC associated with a lack of benefit of abi-
raterone and enzalutamide [101], but no with taxane chemo-
therapy [102,103].
8. Conclusions and Future Perspectives
Despite some limitations of using cfDNA related mainly to the
sensitivity of measuring ctDNA using plasma versus serum
[34] and the different detection methods [76], and lower con-
centration of ctDNA in early disease, plasma DNA is a clini-
cally relevant marker offering new chances for management of
PC patients adding a new helpful tool for diagnosis, staging and
prognosis (Figure 2).
Figure 2. Circulating tumor DNA and other circulating biomarkers in
prostate cancer.
All mCRPC have tumor lesions to detect in plasma matching per-
fectly with tumor tissue.
Future studies are also aimed at the improvement of cancer screen-
ing or as diagnostic biomarkers in early stage disease. In fact, there
are ongoing some clinical trials carried out on early stages of PC.
One study has main objective to evaluate genetic testing in pre-
dicting biomarkers of recurrence in PC patients undergoing sur-
gery (NCT00977457) and two phase 3 trials performing plasma
DNA analysis in PC patients after radiotherapy (NCT01411332
and NCT01411345). Moreover, next studies could also include
patients with localized PC patients receiving neoadjuvant chemo-
therapy predicting pathological residual disease that usually cor-
relates with poor prognosis, as already shown in other tumors. In
the complex scenario of prostate tumor, the detection of ctDNA
may become readily available for routine clinical decision making.
Nowadays, circulating biomarkers are correlated with new imag-
ing techniques, that do not only evaluate tumor extent and distri-
bution, but it can also detect biologic characteristics of all lesions
rather than those of a single biopsy or blood draw. A recent work
[104] made a direct comparison between circulating AR CNV
and 18F-Fluorocholine (FCH) uptake on PET/CT in patients with
metastatic CRPC. AR CNV was determined by digital droplet
PCR and Taqman on pre-treatment plasma from 80 patients with
metastatic CRPC progressing after docetaxel treated with abi-
raterone (n=47) or enzalutamide (n=33). For all patients, an FCH
PET/CT scans was performed. Plasma AR gain was significantly
correlated with tumor metabolic activity. In addition, multivariate
analysis revealed that AR CNV and FCH PET/CT values were as-
sociated with both shorter PFS and OS. These evidences suggested
that choline uptake is higher in AR gained cancers, introducing
the possibility of identifying this molecularly distinct group us-
ing non-invasive imaging, also obtaining further biologic tumor
information performing new tracers, such as Prostate-Specific
Membrane Antigen (PSMA).
In conclusion, the utility of plasma DNA derives from preclinical
and clinical observations and from the integration of circulating
and imaging markers that require, however, larger prospective tri-
als with a clinically meaningful impact in PC patients.
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