Prostate cancer is the second most common cancer and second cause of cancer death in Chilean men [
Prostate specific antigen (PSA) is the only biomarker routinely used for the early detection of prostate cancer. Although PSA is highly specific for prostate, an elevated level is not specific for prostate cancer, being increased in benign pathologies [
We prospectively studied all men undergoing an initial transrectal ultrasound guided (TRUS) prostate biopsy at the Hospital Carabineros of Chile between January 2011 and October 2012. Indications for a TRUS biopsy were an elevated total PSA, defined as >4.0 ng/mL, or a digital rectal examination (DRE) abnormal or suspicious of cancer, defined as the presence of a nodule, areas of indurations, or asymmetry in the size of the lateral lobes [
Mononuclear cells were obtained by differential centrifugation using Histopaque 1,077 (Sigma-Aldrich), washed, and resuspended in 100
CPCs were detected using a monoclonal antibody directed against PSA, clone 28A4 (Novocastro Laboratory, UK), and identified using an alkaline phosphatase-anti alkaline phosphatase based system (LSAB2, DAKO, USA), with new fuchsin as the chromogen. Positive samples underwent a second process with anti-P504S clone 13H4 (DAKO, USA) and were identified with a peroxidase based system (LSAB2, DAKO, USA) with DAB (3, 3′diaminobenzidine tetrahydrochloride) as the chromogen.
A CPC was defined according to the criteria of ISHAGE (International Society of Hemotherapy and Genetic Engineering) [
The discrimination of the differing diagnostic tests was defined using the normal parameters: true positive (TP); false positive (FP), false negative (FN), and true negative (TN). The predictive values, positive (PPV) as well as negative (NPV), were evaluated, as well as the positive and negative likelihood ratios (+LR and –LR, resp.). In men with FN CPC detection the details of the cancer were analyzed. The potential number of biopsies avoided for each method was calculated and the Gleason scores of missed cancers recorded. The diagnostic yield of primary CPC detection was compared with free percent PSA, PSA velocity, and PSA density. A fourth group of combined free percent PSA, PSA velocity, and PSA density was compared, whereby if one parameter of the three was positive the test was considered positive.
In addition, using the criteria of Epstein [
Descriptive statistics were used for demographic variables, expressed as mean and standard deviation in the case of continuous variables with a normal distribution. In case of an asymmetrical distribution the median and interquartile range (IQR) values were used. Noncontiguous variables were presented as frequencies. The Shapiro-Wilk test was used to determine a normal distribution. The Student
303 men participated in the study, with an average age of
Of the evaluated variables, % free PSA, PSA velocity, prostate volume, and PSA density were significantly different between men with positive and negative biopsy (Table
Clinical variables in men with positive and negative initial biopsy.
Positive biopsy | Negative biopsy |
| |
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Age | 65.5 ± 9.8 | 64.8 ± 8.4 |
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PSA ng/mL | 6.10 (IQR 4.67–9.6) | 5.58 (IQR 4.45–7.64) |
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% free PSA | 11% (IQR 9–15%) | 17% (IQR 13–23) |
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PSA velocity ng/mL/yr | 0.85 (IQR 0.59–2.05) | 0.58 (IQR 0.12–1.15) |
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Prostate volume | 44 ± 18 | 57 ± 24 |
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PSA density | 0.17 (IQR 0.11–0.25) | 0.11 (IQR 0.08–0.17) |
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CPC (+) | 100/113 | 22/190 |
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Using the Chi-squared test the frequency of each method to detect cancer or detect no cancer was compared. The results for the differing tests are shown in Table
Absolute detection rates of prostate cancer and no cancer according to test.
Free PSA | PSA velocity | PSA density | Total | CPC | Total | ||||||
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≤15% | >15% | ≥0.75 | <0.75 | ≥0.15 | <0.15 | (+) | (−) | (+) | (−) | ||
Cancer | 80 | 33 | 67 | 46 | 69 | 44 | 97 | 16 | 100 | 13 | 113 |
No cancer | 62 | 128 | 75 | 115 | 60 | 130 | 104 | 86 | 22 | 168 | 190 |
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Use of the tests to define active treatment or active observation in 113 patients with prostate cancer.
Type of |
Free PSA | PSA velocity | PSA density | Total | CPC | |||||
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≤15% | >15% | ≥0.75 | <0.75 | ≥0.15 | <0.15 | (+) | (−) | (+) | (−) | |
Needs treatment | 71 | 24 | 58 | 37 | 61 | 34 | 82 | 13 | 93 | 2 |
Active observation | 9 | 9 | 9 | 10 | 8 | 10 | 11 | 7 | 7 | 11 |
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In the detection of cancers needing treatment, primary CPC detection was significantly superior in comparison with the total PSA parameters (
The diagnostic yields for the 4 PSA based parameters and the detection of primary CPCs are shown in Table
Diagnostic yields for PSA based parameters and primary CPCs.
Sensitivity | Specificity | PPV | NPV | PLR | NLR | |
---|---|---|---|---|---|---|
% free PSA ≤15% | 70.8 (CI 95% 61.5–79.0) | 67.4 (CI 95% 60.2–74.0) | 56.3 (CI 95% 47.8–64.6) | 79.5 (CI 95% 72.4–85.5) | 2.17 (CI 95% 1.71–2.75) | 0.43 (CI 95% 0.32–0.59) |
PSA velocity >0.75 ng/mL/year | 59.3 (CI 95% 49.7–68.4) | 60.5 ( CI 95% 53.2–67.5) | 47.2 (CI 95% 38.8–55.7) | 71.4 (CI 95% 63.8–78.3) | 1.50 (CI 95% 1.19–1.90) | 0.67 (CI 95% 0.52–0.86) |
PSA density ≥0.15 | 61.1 (CI 95% 51.4–70.1) | 68.4 (CI 95% 61.3–75.0) | 53.5 (CI 95% 44.5–62.3) | 74.7 (CI 95% 67.8–81.0) | 1.93 (CI 95% 1.50–2.50) | 0.57 (CI 95% 0.44–0.73) |
Combined | 85.8 (CI 95% 78.0–91.7) | 45.3 (CI 95% 38.1–52.6) | 48.3 (CI 95% 41.2–55.4) | 84.3 (CI 95% 75.8–90.8) | 1.57 (CI 95% 1.35–1.82) | 0.31 (CI 95% 0.19–0.51) |
1° CPCs | 88.5 (CI 95% 81.3–93.7) | 88.4 (CI 95% 83.0–92.6) | 82.0 (CI 95% 73.4–88.3) | 92.8 (CI 95% 88.0–96.1) | 7.64 (CI 95% 5.13–11.38) | 0.13 (CI 95% 0.08–0.22) |
PPV = positive predictive value, NPV = negative predictive value, PLR = positive likelihood ratio, and NLR = negative likelihood ratio.
The number of biopsies that could have been avoided by using the differing parameters and the number of missed cancers using the same criteria are shown in Table
Number of possible avoided biopsies and missed cancers according to the parameter used to determine the need for a prostate biopsy.
Avoided biopsies | Missed cancers |
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% free PSA >15% | 161 (53.1%) | 33 (29.2%) | 113/303 |
PSA velocity <0.75 ng/mL/year | 161 (53.1%) | 46 (40.7%) | 113/303 |
PSA density <0.15 ng/mL | 174 (57.%) | 44 (38.9%) | 113/303 |
CPC negative | 181 (59.7%) | 13 (11.5%) | 113/303 |
Of the missed cancers; using free PSA 15/33 (45.5%) were Gleason 6 or above; using PSA velocity 20/46, (43.5%), PSA density 18/44 (40.9%), and CPC negative 3/13 (23.7%) respectively were Gleason 6 or more cancers. Comparing the frequency of missed cancers Gleason 4 + 5 versus Gleason ≥6 there was no significant difference between the methods (Chi-squared two-tailed test) (Table
Gleason scores (GS) of missed cancers.
GS4 | GS5 | GS6 | GS7 | GS8 | GS9 | Total | |
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Free PSA | 6 | 12 | 7 | 7 | 1 | 0 | 33 |
PSA velocity | 8 | 18 | 8 | 11 | 1 | 0 | 46 |
PSA density | 7 | 19 | 9 | 9 | 0 | 0 | 44 |
CPC negative | 8 | 2 | 1 | 2 | 0 | 0 | 13 |
The results of the biopsies are shown in Table
Patients with false negative CPC result for prostate cancer.
Gleason score | Number of samples positive for cancer | % of sample infiltrated | |
---|---|---|---|
1 | 4 | 2/12 | 5% |
2 | 4 | 2/12 | 5% |
3 | 4 | 2/12 | 7% |
4 | 4 | 1/12 | 5% |
5 | 4 | 2/12 | 5% |
6 | 4 | 1/12 | 5% |
7 | 4 | 2/12 | 15% |
8 | 4 | 6/12 | 50% |
9 | 5 | 4/12 | 50% |
10 | 5 | 2/12 | 3% |
11 | 6 | 1/12 | 2% |
12 | 7 | 4/12 | 15% |
13 | 7 | 1/12 | 30% |
Although total serum PSA measurement has contributed to the early detection and treatment of prostate cancer, it may be elevated in nonmalignant conditions such as benign hyperplasia and prostatitis. With a cut-off value of 4.0 ng/mL, the sensitivity has been reported as being between 67 and 80% but with a specificity of only 20–30% [
For whatever disease a screening test or program must be considered in terms of cost benefit, the benefit being the improvement in mortality and/or morbidity of the disease and the costs being the adverse effects of diagnostic procedures and treatment. In terms of benefits of prostate cancer screening, the results remain controversial. According to the UK NICE guidelines the aim of prostate biopsy is not to detect each and every prostate cancer [
It has been estimated that, of asymptomatic men in whom prostate cancer is detected by prostate biopsy following PSA measurement, around 50% [
A prostate biopsy is not without adverse effects; 0.7% of men biopsied were hospitalized as a result of sepsis and/or hemorrhage [
Thus an ideal biomarker for the detection of prostate cancer is one that detects clinically significant cancers, does not detect indolent cancer, and has a high negative predictive value to avoid unnecessary biopsies.
The study group represents a typical prostate biopsy population, being selected on the basis of a serum total PSA ≤ 4.0 ng/mL with 37% having prostate cancer detected. The values of free % PSA, prostate volume, and PSA density are similar to that reported in Brazilian patients [
The use of PSA velocity as a screening biomarker is due to two recent developments; firstly the results from the Prostate Cancer Prevention Trial shows that there is no single cut-off value of serum PSA that separates men at high risk of prostate cancer or high grade disease from men at low risk [
The detection of primary CPCs had the highest diagnostic yield. It is important to emphasize that the use of primary CPC detection is as a sequential test in men with suspicion of prostate cancer and not as a primary screening test; therefore a direct comparison with performance diagnosis of the serum PSA is not possible.
What is probably more important is that the NPV of 92.8% in a sample of patients with a prevalence of cancer of 37.3% and suspicion of cancer that requires a biopsy showed that the absence of CPCs had a high discriminating power. This suggests that men with an increased serum PSA and/or abnormal DRE but negative CPC could be considered of being at low risk and thus a biopsy might not be necessary. From the point of view of the −LR of 0.13, this permits the reduction of the probability of PC in almost 40% which when applied to a prevalence of approximately 50% significantly reduces the probability of cancer posttest to around 10%. This is clinically useful when determining whether or not to continue investigating.
The test identified 98% of men with clinically significant prostate cancer and was superior to the tests using PSA parameters, alone or in combination. In prostate cancer screening program it is not routine to perform prostatic ultrasound; our data to calculate prostate volume was taken at the time of biopsy and it must be further emphasized that calculated prostate volume may differ up to 25% in comparison with the volume of radical prostatectomy specimen volume. Thus true prostate volume may differ from calculated volume, affecting PSA density values; in this study we did not use a correction factor. PSA velocity has the practical difficulty of at least 1 year of followup and may not be acceptable to patients with an increased PSA value in terms of waiting time to decide for prostate biopsy or not.
Results using the detection of circulating prostate cells and using different methodologies have been discordant. Using a dual PSA/prostate specific membrane antigen RT-PCR method Eschwège et al. [
We believe that part of the difference documented is caused by the relatively high detection in control patients and one explication is that CPC can be found in men with prostatitis; however, these CPCs are P504S negative [
In Chilean men the use of PSA density and/or PSA velocity did not improve the diagnostic yield and free serum PSA was the best of the three PSA parameters used to determine the need for a prostate biopsy in men with an elevated serum total PSA. The use of the three parameters combined improved sensitivity but at the cost of decreased specificity. In comparison the use of the detection of primary CPCs increased the diagnostic yield, decreased the number of biopsies, identified 98% of patients with clinically significant prostate cancer, and did not detect low grade small volume tumors.
The study was approved by the Hospital Scientific Ethical Committee; all patients signed a written informed consent formulary before blood samples were taken.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors wish to thank Mrs. Ana María Palazuelos for her help in the writing of this paper. The study was funded by a grant from the Hospital Carabineros of Chile Research Fund.