Comparing Two Modalities of Screening for Prostate Cancer: Digital Rectal Examination + Transrectal Ultrasonography Vs. Prostate-Specific Antigen

Digital Rectal Examination Is Not a Useful Screening Test for Prostate Cancer

BACKGROUND

Annual digital rectal examination (DRE) is recommended as a stand-alone screening test for prostate cancer (PCa) in Germany for 45+ yr olds. DRE diagnostic performance in men as young as 45 yr old has not been proved by a screening trial.

OBJECTIVE

To determine DRE diagnostic performance in a screening trial.

DESIGN, SETTING, AND PARTICIPANTS

This analysis was conducted within the multicentric, randomized PROBASE trial, which enrolled >46 000 men at age 45 to test risk-adapted prostate-specific antigen (PSA) screening for PCa.

INTERVENTION

(1) DRE was analyzed as a one-time, stand-alone screening offer at age 45 in 6537 men in one arm of the trial and (2) PCa detection by DRE was evaluated at the time of PSA-screen-driven biopsies (N = 578).

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

(1) True-/false-positive detection rates of DRE as compared with PSA screening and (2) DRE outcome at the time of a prostate biopsy were evaluated.

RESULTS AND LIMITATIONS

(1) A prospective analysis of 57 men with suspicious DRE at age 45 revealed three PCa. Detection rate by DRE was 0.05% (three of 6537) as compared with a four-fold higher rate by PSA screening (48 of 23 301, 0.21%). The true-positive detection rate by DRE relative to screening by PSA was 0.22 (95% confidence interval [CI] = [0.07-0.72]) and the false-positive detection rate by DRE was 2.2 (95% CI = [1.50-3.17]). (2) Among PSA-screen-detected PCa cases, 86% had unsuspicious DRE (sensitivity relative to PSA was 14%), with the majority of these tumors (86%) located in the potentially accessible zones of the prostate as seen by magnetic resonance imaging.

CONCLUSIONS

The performance of stand-alone DRE to screen for PCa is poor. DRE should not be recommended as a PCa screening test in young men. Furthermore, DRE does not improve the detection of PSA-screen-detected PCa.

PATIENT SUMMARY

Our report demonstrated the poor diagnostic performance of digital rectal examination in the screening for prostate cancer in young men.

Determining the Sensitivity of Transrectal Ultrasonography on a Consecutive Series of Prostate Cancers in a Clinical and Screening Setting

Purpose

To evaluate the sensitivity at transrectal ultrasonography (TRUS) for prostate cancer.

Material

A consecutive series of 170 prostate cancers identified by matching local cancer registry and TRUS archives at the Centro per lo Studio e la Prevenzione Oncologica of Florence.

Method

TRUS sensitivity was determined as the ratio of TRUS positive to total prostate cancers occurring at different intervals from TRUS date. Univariate and multivariate analyses of sensitivity determinants were performed.

Results

Sensitivity at 6 months, 1, 2 and 3 years after the test was 94.1% (95% Cl, 90-98), 89.8% (95% Cl, 85-95), 80.4% (95% Cl, 74-87) and 74.1% (95% Cl, 68-81%), respectively. A higher sensitivity (statistically significant) of TRUS was observed only if digital rectal examination was suspicious, whereas no association to sensitivity was observed for age, prostate-specific antigen or prostate-specific antigen density.

Conclusions

The study provided a reliable estimate of TRUS sensitivity, particularly reliable being checked against a cancer registry: observed sensitivity was high, at least of the same magnitude of other cancer screening tests. TRUS, which is known to allow for considerable diagnostic anticipation and is more specific than prostate-specific antigen, might still be considered for its contribution to a screening approach.

Reliability of volume or age-adjusted prostate specific antigen to improve diagnostic accuracy

Prostate Specific Antigen (PSA), PSA density, PSA excess, and PSA age-specific range have been compared in 331 subjects (35 cancers, 296 benign) with equivocal findings at screening by PSA or palpation + transrectal ultrasonography. The specificity of PSA using a cut-off of 4 ng/ml was only 0.49. A cutoff of 10 ng/ml improved the specificity to 0.88 but the sensitivity decreased from 0.97 to 0.63. The sensitivity and specificity for PSA density (cutoff 0.15), PSA excess (cutoff -5), and age-specific range were 0.86 and 0.80, 0.80 and 0.82, and 0.91 and 0.67, respectively. Avoided benign biopsies vs missed cancers on the basis of PSA density, PSA excess and PSA age-specific range would have been 19 and 5, 26 and 7, and 16 and 3, respectively. Methods adjusting for prostate volume allow a better interpretation of PSA values and may reduce the benign biopsy rate, but the consequent cost of delayed cancer diagnoses when the choice of biopsy is based only on these methods seems unacceptable.

Thiosulfate in urine as a facilitator in the diagnosis of prostate cancer for patients with prostate-specific antigen less or equal 10 ng/mL

BACKGROUND

The aim of this study was to examine the level of thiosulfate in the urine of prostate cancer (PCa) patients and evaluate its usefulness in the diagnosis and monitoring of prostate malignant transformation. Thiosulfate is a naturally occurring product of hydrogen sulfide (H2S) metabolism. H2S is involved in many physiological and pathological processes including inflammation and tumorigenesis.

METHODS

The determination of thiosulfate in the urine of PCa patients and healthy controls was performed by reverse-phased liquid chromatography using 2-chloro-1-methylquinolinium tetrafluoroborate as a derivatization reagent. Thiosulfate concentrations were normalized to urinary creatinine levels to compensate for variable diuresis.

RESULTS

In the urine samples of PCa patients, the mean thiosulfate level was almost 50 times higher than in the control groups and five times higher than in the benign prostatic hyperplasia group. The level of thiosulfate did not correlate with the serum prostate-specific antigen (PSA) level or PSA density. Neither tumor stage nor tumor grade was associated with thiosulfate level.

CONCLUSIONS

The results suggest that thiosulfate concentration in urine may be a good facilitator in the diagnostics of PCa. The predictive accuracy of this method is particularly valuable for the diagnosis of patients with low serum PSA level and negative digital rectal examination and transrectal ultrasound results.

Proteomic analysis of conditioned media from the PC3, LNCaP, and 22Rv1 prostate cancer cell lines: discovery and validation of candidate prostate cancer biomarkers

Early detection of prostate cancer is problematic due to the lack of a marker that has high diagnostic sensitivity and specificity. The prostate specific antigen (PSA) test, in combination with digital rectal examination, is the gold standard for prostate cancer diagnosis. However, this modality suffers from low specificity. Therefore, specific markers for clinically relevant prostate cancer are needed. Our objective was to proteomically characterize the conditioned media from three human prostate cancer cell lines of differing origin [PC3 (bone metastasis), LNCaP (lymph node metastasis), and 22Rv1 (localized to prostate)] to identify secreted proteins that could serve as novel prostate cancer biomarkers. Each cell line was cultured in triplicate, followed by a bottom-up analysis of the peptides by two-dimensional chromatography and tandem mass spectrometry. Approximately, 12% (329) of the proteins identified were classified as extracellular and 18% (504) as membrane-bound among which were known prostate cancer biomarkers such as PSA and KLK2. To select the most promising candidates for further investigation, tissue specificity, biological function, disease association based on literature searches, and comparison of protein overlap with the proteome of seminal plasma and serum were examined. On the basis of this, four novel candidates, follistatin, chemokine (C-X-C motif) ligand 16, pentraxin 3 and spondin 2, were validated in the serum of patients with and without prostate cancer. The proteins presented in this study represent a comprehensive sampling of the secreted and shed proteins expressed by prostate cancer cells, which may be useful as diagnostic, prognostic or predictive serological markers for prostate cancer.

Relative contribution of digital rectal examination and transrectal ultrasonography in interpreting serum prostate-specific antigen values for screening prostate cancer in Arab men

BACKGROUND

This study was conducted to determine the utility of digital rectal examination (DRE), transrectal ultrasonography (TRUS) and serum prostate-specific antigen (PSA) in the diagnosis of prostate cancer in men in Arabia, an are of the world with a relatively low incidence of this disease.

PATIENTS AND METHODS

329 patients suspected of having prostate cancer on account of raised serum PSA level (>4 ng/ml), DRE or TRUS findings, underwent TRUS-guided prostate biopsy. Raised PSA individually as well as combined, or a lesion suspicious of carcinoma on DRE or TRUS was recorded as PSA(+), DRE(+) or TRUS(+), respectively. The contribution of DRE, TRUS and serum PSA to the diagnosis of prostate cancer was analysed.

RESULTS

Of the 329 patients who had prostate biopsies 109 cases (33.1%) had PCa. Of these 109 patients 56 (51%) had DRE(+), 77 (42%) had TRUS(+) and 49 (66%) had both DRE(+) and TRUS(+). Statistical analysis revealed that DRE(+) tripled the probability for cancer. PSA over a range of 10-50 ng/mL demonstrated an increasing cancer probability ranging from 2 to 3 fold. TRUS(+) was only significantly associated with cancer risk if PSA was elevated. The presence of all three factors increased the cancer probability by 6 to 7 fold.

CONCLUSION

TRUS findings are dependent on PSA for interpretation while DRE(+) with elevated PSA makes PCa more likely.

Discovery of candidate tumor markers for prostate cancer via proteomic analysis of cell culture-conditioned medium

OBJECTIVE

Prostate-specific antigen measurement, widely used for early detection of prostate cancer (CaP), suffers from low specificity. Additional tumor markers are needed for the early detection of clinically relevant CaP. Our objective was to perform a qualitative proteomic analysis of conditioned medium (CM) from the CaP cell line PC3(AR)(6).

METHODS

We used a roller bottle culture system to culture the PC3(AR)(6) cell line in chemically defined serum-free medium for 14 days. By using strong anion-exchange chromatography, we fractionated the CM and trypsinized the fractions. The tryptic peptides were further fractionated by reversed-phase C-18 chromatography before being subjected to electrospray ionization tandem mass spectrometry. We used MASCOT software to search the mass spectra generated and organized identified proteins based on their genome ontology classification of cellular location. We used an immunoassay to measure a newly identified secreted protein, Mac-2BP, and kallikreins 5, 6, and 11 in serum samples from CaP patients and healthy men.

RESULTS

We classified 262 proteins according to cellular location; the sample was found to contain a significant proportion of secreted (23%) and membrane (16%) proteins. In a proportion of cancer patients compared with healthy men, we determined by ELISA that serum concentrations of a novel candidate biomarker Mac-2BP were increased.

CONCLUSIONS

These identified proteins, and possibly many others found in the CM, may have utility as novel CaP biomarkers.

Prostate cancer specific mortality in the Florence screening pilot study cohort 1992–1993

The impact of screening on prostate cancer mortality is still unknown. A favourable impact is suggested by uncontrolled and possibly biased studies. Mortality from all causes and from prostate cancer was assessed in a cohort of 6,861 males aged 60-74 years, participants to a pilot screening study during 1991-1994. Observed/expected mortality was determined by linkage with cancer and mortality registries. Prostate cancer standardised mortality rate (SMR) in the overall series (751 subjects excluded by GPs for disabling illness or prostate cancer; 3,448 refusers, 2,662 attenders; 67,321.2 men-year) was 0.96 (95% confidence interval (CI)=0.74-1.22) when deaths from prevalent cancers diagnosed before screening were considered. Reduced prostate cancer mortality (SMR=0.48; 95% CI=0.26-0.83), persisting beyond five years after study entry (SMR=0.48; 95% CI=0.22-0.90), was observed in attenders and not in refusers (SMR=0.99; 95% CI=0.69-1.37). This finding might suggest a screening effect, but might also be ascribed to an healthy screening effect, and cannot be assumed as a reliable evidence of screening efficacy.

Determining overdiagnosis by screening with DRE/TRUS or PSA (Florence pilot studies, 1991-1994)

The rate of overdiagnosis of prostate carcinoma was assessed by following 6890 participants in pilot screening studies from 1991 to 1994. Observed/expected incidence and mortality were determined using data from the Cancer and Mortality Registry. The cancer detection rate (1.75%) and observed/expected ratio (12.5:1) were high at the first screening, and substantially lower at the second screening (0.65% or 4.10:1). According to the registry follow-up, prostate cancer occurred in 225 subjects in the whole study cohort, while 178.2 were expected with 50652 men/years at risk. The standardised incidence rate was 1.66 in the screened (95%CI=1.4-2.0), 0.97 in the non-responders (95%CI=0.8-1.2) and 1.23 in subjects excluded from invitation due to previous cancer or major illness (95%CI=0.8-1.5). A 66% excess incidence rate was observed in the screened subjects over a 9-year period, confirming previous estimates of overdiagnosis.

Predictors of random sextant biopsy outcome in screened men with PSA > 4 ng/mL and a negative sextant biopsy at previous screening. Experience in a population-based screening program in Florence

The aim of this study was to evaluate possible pedictors of the outcome of repeat random sextant biopsy of the prostate prompted by a rise in prostate-specific antigen (PSA). Random biopsies performed for PSA elevation (>4 ng/mL) in the course of a randomized study of screening efficacy were reviewed, and 87 consecutive biopsies (carcinoma = 13, high-grade prostatic intraepithelial neoplasia = 6, negative = 68) performed in subjects with a negative random biopsy at the previous screening round were considered. Findings at digital rectal examination or transrectal ultrasonography and total PSA value were not useful predictors of repeat biopsy outcome, whereas PSA velocity was significantly associated with biopsy outcome. The positive predictive value for a cancer biopsy was 2.7% (1/36), 28.5% (2/7), and 22.7% (10/44) for PSA velocity values of <0.1, 0.1-0.19, and >0.19 ng/mL/yr, respectively. A cutoff of 0.1 ng/mL/yr for PSA velocity would have allowed to avoid approximately half (35/74 = 47.2%) of the benign biopsies while decreasing the sensitivity by 7.6% (1/13), and is thus suggested as a possible criterion for the indication of repeat random biopsy for persistent PSA elevation.

Prostate cancer screening: the problem of overdiagnosis and lessons to be learned from breast cancer screening

Screening for prostate cancer is a relatively new procedure, still under experimental evaluation within prospective randomised trials. The design of prospective studies has been mainly based on the experience of other cancer screenings, particularly breast cancer, for which data of several controlled studies are available. Unfortunately, breast cancer is very different from prostate cancer, particularly for aspects such as early diagnosis and, thus the screening process, originally modelled on the basis of the lesson taught by breast cancer screening, needs continuous re-evaluation and adjustment, based on data which are now being produced from ongoing screening experiences. In this paper, we will consider the most controversial aspects of prostate cancer screening and compare prostate screening with breast cancer screening in order to promote a better understanding of the current problems and lessons to be learned.

Overdiagnosis of prostate carcinoma by screening: an estimate based on the results of the Florence Screening Pilot Study

OBJECTIVES

To estimate overdiagnosis (detection of latent carcinomas) as a consequence of screening for prostate cancer.

DESIGN

Based on actual screen (first or repeat) detected and interval prostate cancer rates observed in the Florence screening pilot study, a scenario was simulated where males aged 60 years (or 65) had six biennal screens and were followed up for four years. Overdiagnosis was determined as the proportional excess of cancers detected by screening with respect to that expected in its absence.

SETTING

City of Florence, Italy, from 1992 through 1995.

POPULATION

2,740 resident males, aged 60 to 74 years.

RESULTS

Overdiagnosis was estimated to be 51% (95% confidence limits: 44%-55%) or 93% (85%-101%) for age 60 or 65 at entry. Comparison with other screening experiences obtaining higher detection rates suggests that a more aggressive screening approach could be associated with overdiagnosis estimates as big as 200%-250%.

CONCLUSIONS

Screening for prostate cancer is associated with a relevant risk of overdioagnosis. As latent carcinomas can not be presently identified, this would lead to overtreatment in most overdiagnosed cases. The negative consequences of overdiagnosis (knowledge of having a cancer) and of overtreatment (impotence, incontinence, perioperatory death) may be extremely serious. In absence of any scientific evidence of screening benefits (if any) screening should not be recommended as a current practice, but should be limited to prospective controlled studies designed to assess its cost-effectiveness.