PSA screening for prostate cancer: the current controversy

Diagnosis of prostate cancer via nanotechnological approach

Prostate cancer is one of the leading causes of cancer-related deaths among the Caucasian adult males in Europe and the USA. Currently available diagnostic strategies for patients with prostate cancer are invasive and unpleasant and have poor accuracy. Many patients have been overly or underly treated resulting in a controversy regarding the reliability of current conventional diagnostic approaches. This review discusses the state-of-the-art research in the development of novel noninvasive prostate cancer diagnostics using nanotechnology coupled with suggested diagnostic strategies for their clinical implication.

Role of tumor markers in patients with solid cancers: A critical review

The measurement of tumor markers is currently one of the most rapidly growing areas in laboratory medicine. Lack of sensitivity and specificity preclude the use of most existing markers for the early detection of malignancy. For patients with diagnosed malignancy, however, markers are potentially useful in determining prognosis, predicting therapeutic response, maintaining surveillance following curative surgery and monitoring therapy in advanced disease. Clinically useful markers include CEA in the surveillance of patients with diagnosed colorectal cancer, AFP and HCG in the management of patients with non-seminomatous germ cell tumors, HCG in the management of patients with trophoblastic disease, CA 125 for monitoring therapy in patients with ovarian cancer, estrogen receptors for predicting response to hormone therapy in breast cancer and HER-2 for the identification of women with breast cancer likely to respond to trastuzumab (Herceptin). Although widely used, the impact of PSA screening in reducing mortality from prostate cancer remains to be shown.

Hypermethylation of the CpG islands in the promoter region flanking GSTP1 gene is a potential plasma DNA biomarker for detecting prostate carcinoma

OBJECTIVES

To investigate the possibility of identifying DNA hypermethylation in the circulation of prostate cancer patients.

METHODS

Plasma DNA samples were extracted from 36 prostate cancer patients and 27 benign prostate hyperplasia (BPH) cases. After extensive methylation-sensitive restriction enzyme digestion, the DNA samples were subjected to the real-time quantitative PCR amplification. Dissociation curve analysis was applied to determine if hypermethylation occurred in the promoter region flanking the GSTP1 gene, a well-documented epigenetic event among prostate cancer cells, in these plasma DNA samples.

RESULTS

11 of 36 prostate cancer patients showed positive peak pattern, indicating methylation changes occurred. Concordant data were obtained from the corresponding paraffin-embedded tissue samples available from the Tumor Bank. Twenty-five of the 27 BPH cases showed negative results, suggesting no methylation changes happened in the CpG islands in these cases.

CONCLUSIONS

We have successfully identified prostate cancer genome hypermethylation in the peripheral circulation in prostate cancer patients with this protocol. This method can effectively distinguish BPH from prostate neoplasm. Although a larger number of samples are necessary to validate the capability of the protocol in practice, using plasma DNA sample is an ideal non-invasive approach for prostate neoplasm detection.

Selenium and prevention of prostate cancer in high-risk men: the Negative Biopsy Study

Epidemiological and clinical studies suggesting a significant inverse relationship between intake of dietary selenium and overall cancer risk have led to initiation of a randomized, placebo-controlled, phase III clinical trial testing the safety and efficacy of selenized yeast as a chemopreventive agent for prostate cancer. Participants eligible for the 'Negative Biopsy Study', which was initiated in August 1999, are men considered to be at high risk for prostate cancer because of at least one negative sextant prostate biopsy, which was clinically indicated within 1 year of enrollment to the study. After a 30-day run-in period to ensure protocol compliance, participants are randomized to receive either 200 or 400 microg selenized yeast or matched placebo once daily. Primary study endpoints include development of prostate cancer and prostate-specific antigen (PSA) velocity. Secondary biochemical endpoints include change in chromagranin A and alkaline phosphatase. As of 1 June 2003, 514 eligible participants had been enrolled. Randomization schema was effective for selected parameters including age, body mass index, smoking status, baseline PSA and baseline plasma selenium level. Various data, including medical history, family history, and urological symptoms and specimens (including blood and subsequent prostate biopsy samples) had been collected at baseline, and throughout both the intervention and follow-up stages of the protocol. The goal for accrual is 700 evaluable participants.

Serendipity in detecting disease in low prostate-specific antigen ranges

OBJECTIVE

To assess the magnitude of prostate cancer detection by serendipity (the coincidental detection of prostate cancer during the evaluation of an abnormal screening test result) when a digital rectal examination (DRE) and transrectal ultrasonography (TRUS) are used as initial screening tests for prostate cancer in men with low levels of prostate-specific antigen (PSA; 0.0-3.9 ng/mL).

PATIENTS AND METHODS

In all, 117 participants of a population-based screening study were diagnosed with prostate cancer after a standard evaluation of an abnormal screening test result; 49 underwent radical prostatectomy. Serendipity was defined as either: (i) the presence of prostate cancer opposite to the side that raised suspicion for cancer on DRE and/or TRUS; (ii) a negative lesion-directed biopsy while cancer was present in one or more of the cores of the sextant biopsy; (iii) a tumour volume of < 0.5 mL on radical prostatectomy.

RESULTS

Depending on the definition, 27-63% of prostate cancers detected at low PSA values were detected coincidentally and not as a result of a true-positive test result. The proportion of cancers detected by serendipity was inversely correlated with serum PSA level.

CONCLUSION

A relatively high proportion of prostate cancers diagnosed in men with low PSA levels, and in which a biopsy was prompted by a suspicious DRE and/or TRUS, are considered to be detected by chance only. As these cancers are mostly small (< 0.5 mL), with potentially low biological aggressiveness, relying on serendipity seems disadvantageous in prostate-cancer screening. The level of serendipity in prostate cancer detection, the poor performance of the screening test, and high inter-observer variability, casts further doubt on the utility of DRE (and TRUS) as initial screening tests for prostate cancer in population-based screening.

PSA-use in a Spanish industrial area

OBJECTIVES

To document the extent of prostate-specific antigen (PSA)-testing in the general population at Getafe (Spain) outside our prostate cancer (PC) screening program, and to check its performance in terms of PC detection.

METHODS

A total of 5371 PSA-test records (1997-1999) were reviewed and testing rates estimated per 1000 person-years. The extent of patient referral (men referred to our facilities) was calculated adjusting for PSA levels. To approach the performance of testing in the general population, our PC screening program acted as a standard for comparison. The probability of missing one PC in the general population was estimated in terms of number of men necessary to screen (NNS). Calculations were made adjusting for PSA levels.

RESULTS

PSA-testing rate in the general population was 21.6/1000 person-years. In the age-group 55-69 years, this rate was 86.8/1000 (152.6 in men >70 years). Referral rates were 67.9 and 39.5% for men with PSA 4-10 and >10 ng/ml, respectively. Overall PC detection rate was 1.76%. Detection rates for PSA 4-10 and >10 ng/ml were 4.66 and 12.94%, respectively. When compared with the performance of the screening program, for every 17 men with a PSA in the range 4-10 ng/ml one cancer was missed (95% confidence interval (CI), 9-580). Similarly, one cancer was lost for every four men with a PSA >10 ng/ml (95% CI, 2-8).

CONCLUSIONS

The extent of opportunistic testing in our setting is very high, particularly in the older age groups. Opportunistic screening renders PC detection rates lower than expected for every PSA level and cannot be encouraged.

Screening for prostate cancer with prostate-specific antigen: beware the biases

BACKGROUND

The evidence relating to the use of prostate-specific antigen (PSA) as a screening test is a highly controversial, as demonstrated by the lack of agreement among experts. There may be biases associated with various studies.

ISSUES

The main controversy is the relatively high prevalence of prostate cancer (PC) found at autopsy compared with the relatively low death rate from the disease. The lack of modifiable risk factors has led to early detection as a strategy to reduce mortality, as there is evidence for a significant burden of disease. Important issues are the accuracy of current screening tests, some attempts to improve on them, and whether there are good prognostic markers. The consequences of PSA testing (usually further testing including biopsy) and outcomes of treatment are presented in terms of mortality and morbidity; quality of life (QOL) must also be considered. Also important are the benefits from, and the difficulties associated with the "informed choice" approach to PSA screening.

CONCLUSION

There is evidence to suggest that biases can have a significant impact on the utility of PSA as a screening test for PC.

[Analysis of the use of prostate specific antigen (PSA) in a health area of the Community of Madrid]

OBJECTIVES

To approach the local extent of PSA-use, and to check its yield in terms of prostate cancer (PC) detection.

METHODS

All PSA-test records (1997-1999) were reviewed and testing rates calculated per 1000 person-years. Detection rate (PC) was also estimated and referred to our PC prevalence study using the odds ratio as instrument for comparison.

RESULTS

Testing rate in the general population was 21.6/1000 person-years. PC detection rate was 1.76% (1.28 inside the prevalence study). For every CP detected in the general population with a PSA ranging 4-10 ng/ml, 2.39 (OR = 2.39) were detected in the prevalence study (OR = 4.48 for the PSA range > 10 ng/ml).

CONCLUSIONS

PSA-testing in our setting is high. PC detection rates were lower than expected.

Prostate cancer in Austria: impact of prostate-specific antigen test on incidence and mortality

The aim of the study was to assess the impact of prostate-specific antigen (PSA) testing on prostate cancer mortality in Austria. A join-point regression model and permutation tests were used to identify changes in the slope of age-specific trends respectively calculating the annual percentage change (APC). Age-adjusted incidence increased (P < 0.01) between 1983 and 1997 by 79% from 52.2 to 93.6 cases per 100 000 men/year. Incidence in localized/regional stage disease increased in all ages by 143% from 25.7 to 62.4 cases per 100 000 men/year. Incidence in distant disease decreased (P < 0.01) between 1983 and 1997 in all ages by 38% from 9.5 to 5.9 cases per 100 000 men/year. Incidence in unstaged disease increased (P < 0.01) between 1983 and 1997 in all ages by 300% from 4.5 to 18 cases per 100 000 men/year. Age-adjusted mortality increased (P < 0.05) by 13% from 26.8 in 1983 to 30.3 deaths per 100 000 men/year in 1999. No significant changes of trends in mortality rates were detected in the age groups 50-59 years. In the age group 70-79 years the trend changed (P < 0.05) direction in 1991 and in 1994; 1983 through 1991 APC = 3.52 (95% CI 1.37, 5.72), 1991 through 1994 APC = -10.27 (95% CI -26.20, 9.1) and 1994 through 1999 APC = -0.25 (95% CI -4.55, 4.24). PSA testing increased incidence but no impact on mortality in the target population can be observed so far.

Clinical uses of tumor markers: a critical review

Tumor markers are molecules that indicate the presence of malignancy. They are potentially useful in cancer screening, aiding diagnosis, assessing prognosis, predicting in advance a likely response to therapy, and monitoring patients with diagnosed disease. Because of the low prevalence of most cancers in the general population and the limited sensitivity and specificity of available markers, these tests alone are generally of little value in screening for cancer in healthy subjects. Currently, however, PSA in combination with digital rectal examination and CA 125 together with ultrasound are undergoing evaluation as screening modalities for prostate and ovarian cancer, respectively. Again, because of a lack of sensitivity and specificity, markers are rarely of use in the early diagnosis of cancer. As prognostic indicators, markers may provide information that is independent of traditionally used factors or within subgroups defined by traditional criteria, for example, urokinase plasminogen activator in node-negative breast cancer. At present, the best available marker for predicting response to therapy is the estrogen receptor for selecting hormone-sensitive breast cancers. Many different markers can be used in the surveillance of patients with diagnosed malignancies, the most useful of these being HCG in trophoblastic disease and both AFP and HCG for nonseminomatous testicular germ cell tumors. In general, the currently available tumor markers lack sensitivity for early cancer and specificity for malignancy. The goal of future research should be to develop more sensitive and specific markers, especially for the common cancers.

Measurement of Circulating Forms of Prostate-specific Antigen in Whole Blood Immediately after Venipuncture: Implications for Point-of-Care Testing

Background: The purpose of this study was to validate the use of whole-blood samples in the determination of circulating forms of prostate-specific antigen (PSA).

Methods: Blood samples of hospitalized prostate cancer and benign prostatic hyperplasia patients were collected and processed to generate whole-blood and serum samples. Three different rapid two-site immunoassays were developed to measure the concentrations of total PSA (PSA-T), free PSA (PSA-F), and PSA-α1-antichymotrypsin complex (PSA-ACT) to detect in vitro changes in whole-blood samples immediately after venipuncture. The possible influence of muscle movement on the release of PSA from prostate gland was studied in healthy men by measuring the rapid in vitro whole-blood kinetics of PSA forms before and after 15 min of physical exercise on a stationary bicycle.

Results: Rapid PSA-T, PSA-F, and PSA-ACT assays were designed using a 10-min sample incubation. No significant changes were detected in the concentrations of PSA-T, PSA-F, and PSA-ACT from the earliest time point of 12–16 min compared with measurements performed up to 4 h after venipuncture. Physical exercise did not influence the concentrations of the circulating forms of PSA. Hematocrit-corrected whole-blood values of PSA-T and PSA-F forms were comparable to the respective serum values. Calculation of the percentage of PSA-F (PSA F/T ratio × 100) was similar irrespective of the sample format used, i.e., whole blood or serum.

Conclusions: We found that immunodetectable PSA forms are likely at steady state immediately after venipuncture, thus enabling the use of anticoagulated whole-blood samples in near-patient settings for point-of-care testing, whereas determinations of PSA (e.g., PSA-T, PSA-F, or PSA-ACT) performed within the time frame of the office visit would provide results equivalent to conventional analyses performed in serum.

Health-related quality of life in patients with screen-detected versus clinically diagnosed prostate cancer preceding primary treatment

BACKGROUND

The purpose of this study was to evaluate baseline health-related quality of life (HRQOL) in patients with localized prostate cancer before primary treatment (radical prostatectomy or radiotherapy).

METHODS

Two hundred patients with newly diagnosed localized (screen-detected or clinically diagnosed) prostate cancer completed HRQOL questionnaires (generic and disease-specific measures). Clinical data were collected from patients' medical records in four Rotterdam hospitals.

RESULTS

Screen-detected tumors were of more favorable stages and grades than clinically diagnosed ones. The diagnostic groups did not differ significantly in bowel and sexual functioning. Differences were found in urinary functioning, favoring patients with screen-detected tumors of T2-T3 stages. Patients with screen-detected T2 cancer reported better generic HRQOL (physical aspects) than the clinical group, but HRQOL of the latter group was similar to the population norm. Radiotherapy patients were significantly older and had more comorbidity than subjects referred to prostatectomy. Urinary, bowel, and sexual problems were uncommon. Older (> 65 years) radiotherapy patients appeared to be less sexually active. Radiotherapy patients also reported poorer levels of generic HRQOL.

CONCLUSIONS

Screen-detected prostate cancer patients presented with more favorable cancer stage and grade. HRQOL was related to both the tumor stage and the detection method. Pre-treatment HRQOL differences between prostatectomy and radiotherapy patients were associated neither with tumor characteristics nor with the detection method. Baseline differences in HRQOL should be taken into account when evaluating post-treatment HRQOL.

Silencing of CD44 expression in prostate cancer by hypermethylation of the CD44 promoter region

Loss of the CD44 transmembrane glycoprotein in primary prostate cancer has been shown to be associated with unfavorable clinical behavior. Moreover, the majority of prostate cancer metastases lack expression of this molecule. The mechanism of CD44 silencing in prostate cancer was investigated using both patient material and in vivo-propagated human prostate cancer xenografts. In 9 of 11 lymph node metastases of prostate cancer, we demonstrated by methylation-sensitive restriction enzyme digestion that the promoter region of the CD44 gene is methylated, indicating that this represents a major mechanism of CD44 silencing. Similarly, in 6 out of 12 in vivo-growing human prostate carcinoma xenograft models, hypermethylation of the CD44 gene was found. The extent of CpG island methylation was investigated by nucleotide sequencing after bisulphite modification of the CD44 promoter region. In the xenografts displaying hypermethylation, the examined 14 CpG sites in the CD44 transcription regulatory domain, including a Sp1 binding site, were consistently methylated. This correlated with reduced CD44 expression or lack of CD44 expression at mRNA and protein levels. In the xenografts lacking hypermethylation of the CD44 gene, high levels of CD44 mRNA and protein were expressed in some models, whereas in others CD44 mRNA expression was only detectable by RT-PCR and the CD44 protein could hardly be detected or was not detected at all. The results indicate that, in most prostate cancers, loss of CD44 expression is associated with extensive hypermethylation of the CpG island of the CD44 promoter region, but other, posttranscriptional mechanisms may also lead to CD44 loss.