NOVEL PROSTATE CANCER ANTIGEN 3 (PCA3) BIOMARKER
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ATHANASIOS G. PAPATSORIS, MICHAEL CHRISOFOS, ELENI EFSTATHIOU, ANDREAS
SKOLARIKOS, CHARALAMBOS DELIVELIOTIS
Department of Urology (AB, AGP, MC, AS, CD), Sismanoglio Hospital, Athens,
Greece and University Department of Clinical Therapeutics (EE), Alexandra
Hospital, Athens, Greece
Vol. 36 (6):
665-669, November - December, 2010
is a prostate specific, nonprotein coding RNA that is significantly over
expressed in prostate cancer, without any correlation to prostatic volume
and/or other prostatic diseases (e.g. prostatitis). It can now easily
be measured in urine with a novel transcription-mediated amplification
based test. Quantification of PCA3 mRNA levels can predict the outcome
of prostatic biopsies with a higher specificity rate in comparison to
PSA. Several studies have demonstrated that PCA3 can be used as a prognostic
marker of prostate cancer, especially in conjunction with other predictive
markers. Novel PCA3-based nomograms have already been introduced into
clinical practice. PCA3 test may be of valuable help in several PSA quandary
situations such as negative prostatic biopsies, concomitant prostatic
diseases, and active surveillance. Results from relevant clinical studies,
comparative with PSA, are warranted in order to confirm the perspective
of PCA3 to substitute PSA.
words: prostatic neoplasms; biopsy; PCA3; PSA; tumor marker
Int Braz J Urol. 2010; 36: 665-9
its approval by the US Federal Drug Administration in 1986, prostate-specific
antigen (PSA) has been employed worldwide to diagnose and monitor men
with prostate cancer (PCa) (1). Unfortunately, PSA bears a low positive
predictive value, resulting in a significant proportion of negative biopsies,
often leading to repeat PSA measurements and biopsies. In men with serum
PSA between 3-10 ng/mL (grey zone) the negative biopsy rate is approximately
60-75% (1). Moreover, PSA-based opportunistic screening has led to an
increase in PCa diagnosis and over treatment due to the high incidence
of clinically insignificant PCa (2). Furthermore, men that undergo a PSA
test and a consequent biopsy experience anxiety over the result and the
outcome (3). Therefore, there is a need for PCa biomarkers with a better
specificity to enter clinical practice. Such a perspective biomarker is
prostate cancer antigen 3 (PCA3).
WHAT IS PCA3?
1995, PCA3 was identified in collaborative research effort by Johns Hopkins
Hospital, Baltimore and the Radboud University, Nijmegen, Netherlands
(4). Initially, it was called Differential Display clone 3 (DD3) as differential
display analysis was used to compare mRNA expression patterns of normal
versus cancerous prostatic tissue (5). PCA3 is a segment of non-coding
messenger ribonucleic acid (mRNA) from chromosome 9q21-22 (5). The multiplicity
of stop codons across the three reading frames of PCA3 and the lack of
an extended open reading frame indicates that PCA3 functions as a non-coding
RNA without encoding a protein (6). Recently, a new genomic structure
of PCA3 as well as new flanking and overlapping gene transcripts (e.g.
PCA3-TS4 isoform) have been identified (7).
PCA3 is over expressed by more than 95%
of all prostate cancers tested (5). It can determine benign from cancerous
prostate cells with an accuracy approaching 100% (8). Furthermore, no
PCA3 transcripts have been detected in extraprostatic tissues (benign
and cancerous), demonstrating that PCA3 is the most specific PCa biomarker
identified to date (8). Unlike serum PSA, PCA3 is not affected by age,
prostate volume or other prostatic diseases (e.g. prostatitis) (5,7).
is measured in urine samples collected after an attentive digital rectal
examination (DRE) of the prostate in order for cells to exfoliate in urine.
A DRE of three (more strokes share equivalent results) strokes per lobe
is performed by applying firm pressure (surface is depressed by approximately
1 cm) from the base to apex and from the lateral to the median line for
each lobe (9). Without DRE the PCA3 test provides valid results in only
approximately 80% of cases (5,7).
The PCA3 test requires collection of the
first 20-30 mL of voided urine after DRE. Approximately 2 mL of the urine
sample is placed into a transport tube with lysis buffer that contains
ribonuclease inhibitors (mRNA is destroyed within 20 minutes in the absence
of the inhibitors) (8). The transport tube is sent overnight to a specialized
laboratory at room temperature but it can also be stored frozen. Some
authors use urinary sediments instead of urine samples in order to examine
all the cells and cell fragments (10). However, due to simplified procedures
whole urinary samples are preferred (10).
Three successive generations of the PCA3
test have been presented, leading to a commercially available kit known
as the ProgensaTM PCA3 assay (Gen-Probe, San Diego, CA, USA) (11). Fortunately,
this novel fast and easy transcription-mediated amplification (TMA)-based
test has replaced the older intensive and time-consuming reverse-transcriptase
polymerase chain reaction test (5). The TMA-based PCA3 assay consists
of the following steps: i) specific isolation of the RNA of interest by
using coated magnetic beds, ii) amplification, and iii) detection and
quantification of the isolated RNA (11). Informative rates (percentage
of urine samples yielding accurately quantifiable mRNAs for assay) are
> 99% and the assays have good reproducibility (12).
The PCA3 assay provides a quantitative result
from the ratio of the mRNA transcripts of PCA3 to PSA. The quantification
of PSA mRNA is required to normalize the total mRNA present in a sample.
The PSA mRNA levels in prostate cells released in urine are unrelated
to PSA protein levels in blood and are essentially unchanged in prostate
cancer (12). The PCA3 score is the ratio of PCA3:PSA mRNAs multiplied
by 1,000 (5).
The PCA3 score correlates with the results
of a subsequent prostatic biopsy as a high score increases the likelihood
of a PCa positive result. It has been demonstrated that men with a PCA3
score < 5 had a PCa positive biopsy rate of 14%, while 69% of men with
a PCA3 score > 100 had PCa upon biopsy (5). A cutoff PCA3 score of
35 has been adopted because in a prospective study among 570 men undergoing
prostate biopsy, this score combined the greatest cancer sensitivity and
specificity (54% and 74%, respectively) (13).
test may be of valuable help in the following PSA quandary conditions:
i) elevated PSA with one or more negative biopsies, ii) normal PSA with
family history of prostate cancer, iii) normal PSA with positive biopsy,
iv) elevated PSA with prostatitis, v) elevated PSA with precursor lesions
of PCa (14), and vi) active surveillance for presumed microfocal disease
(15). Potential clinical applications include the detection of local recurrence
following radical prostatectomy or radiotherapy and monitoring patients
on medication that affects serum PSA (i.e. 5-alpha reductase inhibitors)
Recently, in a review (11) of clinical studies with 2048 men undergoing
a first or repeat biopsy, the area under curve (AUC) for PCA3 was 0.66-0.87,
while the AUC for PSA always scored less. In comparison with PSA, the
specificity of PCA3 was better (66-89%), while the sensitivity was less
(54-82%). The positive (48-75%) and negative (74-90%) predictive values
were better for PCA3. In the cohort of 1125 patients with at least one
negative biopsy, PCA3 proved (multivariate analysis) to be an independent
predictive factor of repeat positive biopsy.
Can PCA3 be considered a prognostic marker
for PCa? The association of PCA3 with prostatectomy tumor volume and other
clinical/pathological features was assessed by several authors. In most
studies PCA3 was significantly correlated with tumor volume, pT stage
and Gleason score (GS) (11). Moreover, PCA3 was significantly higher in
patients with clinical significant PCa (dominant tumor volume > 0.5
cc and GS = 7) (5). However, recently the predictive value of PCA3 for
PCa aggressiveness as reported in earlier studies was not confirmed in
a study among 70 men who underwent radical prostatectomy (2). This could
be attributed to the usage of urinary sediments instead of whole urine
samples and to the small number of patient’s favorable prognostic
outcome. The prognostic value of PCA3 needs validation in definitive trials.
PCA3 was identified as a statistically independent
and informative novel marker that is capable of increasing the predictive
accuracy of multivariate biopsy models (16). Predictive accuracy estimates
of biopsy outcome predictions were quantified using the AUC of the receiver
operator characteristic analysis in models with and without PCA3. Recently,
a PCA3-based nomogram has been presented by Chun et al. (16) that identifies
men at risk of harboring PCa and it assists in deciding whether further
evaluation is necessary. When PCA3 is combined with serum PSA and biopsy
GS, it increased diagnostic accuracy to 90% to predict extracapsular extension
or clinically low volume (< 0.5 cc) tumor (17). Patients with a biopsy
GS of 6, low PSA and a low PCA3 could be excellent candidates for active
The incorporation of PCA3 data into the
Prostate Cancer Prevention Trial (PCPT) risk calculator showed additional
benefit (18). PCA3, PSA and DRE data from 521 men undergoing prostate
biopsy were included in the original PCPT risk calculator. The AUC for
the updated PCPT calculator was 0.7, which was statistically superior
to the AUC (0.61) of original PCPT calculator without the PCA3. Furthermore,
the sensitivity, positive and negative predictive value were improved
with the incorporation of the PCA3.
Lastly, patients with precursor lesions of PCa (prostatic intraepithelial
neoplasia, atypical small acinar proliferation) had a significant higher
mean PCA3 score, in comparison with men with negative biopsy results (11,14).
Nearly one third of patients with a negative biopsy and a PCA3 score >
35 had high-grade prostatic intraepithelial neoplasia (19).
fulfils many of the requirements for PCa biomarker to be useful in clinical
practice: i) an easily accessible biological sample (urine after DRE),
ii) a reproducible technique across testing laboratories (aided by an
available commercial kit), and iii) good statistical accuracy (substantiated
by several teams studying populations of different origins) (11). One
efficient way to use PCA3 as a guide to choosing repeat biopsy is to collect
a PCA3 sample at the time of prostate biopsy (“reflex PCA3”)
(20). If the biopsy finding is negative, the PCA3 test can be performed
without the patient having to return.
Because PCa is a heterogeneous disease, the use of a panel of biomarkers
(e.g. PCA3 and TMPRSS2-ERG gene fusions) can further improve diagnostic
accuracy (6). The challenge remains to identify biomarkers that can contribute
to identify potentially life-threatening PCa at a curable stage. PCA3
could be such a potential prognostic marker but results from relevant
research are warranted.
CONFLICT OF INTEREST
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March 4, 2010
Dr. Athanasios G. Papatsoris
University Department of Urology
Athens, 15126, Greece
In the review
article by Bourdoumis et al., the clinical utility of prostate cancer
antigen 3 (PCA3) as a diagnostic marker for prostate cancer is highlighted.
Currently, prostate cancer screening guidelines have failed to take a
strong position on the merits of prostate cancer screening due in large
part to the ongoing controversies on the survival benefit imparted from
prostate cancer screening using a combination of digital rectal examination
and serum prostate-specific antigen (PSA) level measurements (1). In consequence,
clinicians have been seeking a better diagnostic and prognostic test for
The preliminary studies evaluating the diagnostic utility of PCA3 would
suggest that it may have great potential either as a substitute or adjunctive
clinical tool for patients suspected of harboring prostate cancer and
hence, requiring transrectal ultrasound guided prostatic biopsies. Prior
to making more definitive recommendations on the role of PCA3 as a screening/diagnostic
tool for prostate cancer, a multi-institutional prospective clinical trial
comparing PSA and PCA3 will be required. Similarly, we are currently embarking
in a new era of medicine in which a personalized approach to patient care
can be adapted utilizing not only conventional clinical parameters but
as well tumor cytoarchitectural and tissue expression patterns (2).
As clinicians, we are constantly seeking better diagnostic and therapeutic
tools to help tailor treatment recommendations based on tumor aggressivity
and risk of progression while taking into account treatment related morbidity
and quality of life.
This discussion is particularly pertinent for prostate cancer as we clearly
know that a significant proportion of patients have clinically insignificant
disease and may be candidates for active surveillance. Clinical tools
enabling us to identify patients at low risk of disease progression may
change the treatment paradigm. In consequence, aggressive local therapy
can therefore be offered to those best suited.
GL, Crawford ED, Grubb RL 3rd, Buys SS, Chia D, Church TR, et al.: Mortality
results from a randomized prostate-cancer screening trial. N Engl J
Med. 2009; 360: 1310-9. Erratum in: N Engl J Med. 2009; 360: 1797.
MJ, Khan FM, Fernandez G, Mesa-Tejada R, Sapir M, Zubek VB, et al.:
Personalized prediction of tumor response and cancer progression on
prostate needle biopsy. J Urol. 2009; 182: 125-32.
Philippe E. Spiess
Division of Urology
H. Lee Moffitt Cancer Center
Tampa, Florida, USA