[Epidemiology of prostate cancer: recent results from the Epidemiological Cancer Register of the District of Münster (Germany)]. / Aktuelle Daten zur Epidemiologie des Prostatakarzinoms : Ergebnisse aus dem Regierungsbezirk Münster.

BACKGROUND: Prostate cancer is characterized by worldwide increasing incidence rates, improved survival, and decreasing mortality. We investigated the current situation in the Epidemiological Cancer Register of the District of Münster, Germany (which has approximately 1.25 million male inhabitants). MATERIALS AND METHODS: We calculated the incidence and mortality rates, stage distribution, and relative survival rates for prostate cancer between the years 2002 and 2004. RESULTS: The age-standardized incidence rate was 115/100,000 men per year, and the median age at diagnosis was 70 years. The tumour stage was T1/T2 in 69.6% of cases. The estimated relative survival after 5 years was 83.5% (95% confidence interval 81.4-85.4) and after 10 years was 73.3% (69.5-77.0). Survival was barely affected when the tumour was limited to the prostate (UICC I-II), whereas survival rates were markedly reduced when the tumour had spread or had infiltrated adjacent structures (UICC IV; relative 10-year survival rate 22.1%). CONCLUSIONS: The majority of patients with prostate cancer now have a favourable prognosis. Increased incidence rates must be interpreted in the context of widespread use of prostate-specific antigen testing.

[DiaPat urine test for prostate cancer. Predictive value for results of transrectal ultrasound-guided prostate biopsies]. / DiaPat-Prostatakarzinom-Urintest. Vorhersagekraft für das Ergebnis transrektal-sonographisch gesteuerter Prostatabiopsien.

BACKGROUND: A novel urine test for early detection of prostate cancer (PCA), distributed and marketed by the company DiaPat, is advertised by the statement "correct analysis in 9 of 10 cases." PATIENTS AND METHODS: The test separates urinary polypeptides by means of capillary electrophoresis and characterizes the peptides in a time-of-flight mass spectrometer. The DiaPat test was performed on the urine of 18 men prior to multiple ultrasound-guided prostate biopsies. RESULTS: Sixteen of the 18 samples met the requirements for sample quality as established by the manufacturer. Eight of these 16 urine samples had been collected from patients in whom biopsies consecutively detected PCA; the remaining eight patients had benign biopsy results. Among the eight patients with detected PCA, the urine test yielded a low probability for PCA in three cases and a high probability in five. Within the group of eight patients with benign biopsy results, the urine test predicted a high probability for PCA in five men and a low probability in three. For the given PCA incidence of 50% within the investigated population, the DiaPat test correctly predicted biopsy results in one half of the population, whereas prediction in the remaining half was incorrect. CONCLUSION: Unless reliable validation of the DiaPat urine test for PCA is available, no clinical consequences should be drawn from the test results.

[Practice of early detection of prostate cancer : Descriptive survey in preparation for the PSAInForm study]. / Praxis der Früherkennung des Prostatakarzinoms : Deskriptive Erhebung im Vorfeld der PSAInForm-Studie.

BACKGROUND: The randomized controlled PSAInForm study aims to investigate the effects of a computer-based decision aid which informs men in the age group 55-69 years about advantages and disadvantages of PSA testing. In preparation for the study, the current PSA testing practice in the Münster district was assessed. MATERIALS AND METHODS: The frequencies of early detection examinations, medically indicated PSA tests, and prostate biopsies in the Münster district were determined, using aggregated data from the regional association of Statutory Health Insurance (SHI) Physicians in Westfalen-Lippe. With anonymized laboratory data, the frequency of PSA tests in general and urological practices, and their distribution among the accounting categories SHI, individual health services, and invoices for privately insured patients were investigated. RESULTS: In about half of more than 50,000 PSA tests, the accounting category could be determined; the rest could only be assigned to SHI or non-SHI services. The percentage of PSA tests that were performed due to reasons other than medically necessary SHI-reimbursed services was > 50% in each age group; it was highest in men younger than 55 years, and declined markedly with advanced age. More than half of the PSA tests that were likely due to opportunistic screening were performed outside the age group 55-69 years. CONCLUSIONS: The percentage of PSA tests that were not carried out as SHI services was > 80% in general practices, and 60% in urological practices. These percentages decreased markedly with advancing age. Most of the PSA tests were performed outside the age group which can be considered as the target group for an effective PSA screening according to the results of the European Randomized study of Screening for Prostate Cancer (ERSPC).

Implementation of a map in radical prostatectomy specimen allows visual estimation of tumor volume.

INTRODUCTION: Tumor volume is one of the best documented prognostic factors for prostate cancer. There are several methods to gain this important parameter but unfortunately most of the clinicians in the world do not get this information in their routine practice from the pathologist. We developed a standardized method to handle radical prostatectomy specimens including a special form of mapping in order to document relevant morphological data. The aim of this study was to investigate if our model of mapping prostate cancer, which we use in routine practice, may serve for visual estimation of tumor volume. METHODS: We estimated the tumor volume of prostate cancer by visual estimation of 350 maps of radical prostatectomy specimens and correlated these data with established prognostic parameters and clinical outcome. RESULTS: Significant correlations between tumor volumes, as obtained from our mapping, and known prognostic parameters such as preoperative serum levels of prostatic specific antigen, loss of differentiation, histological grade, lymph node metastasis, and margins were found. In a multivariate analysis, only Gleason score and tumor stage were shown to be independent prognostic parameters. DISCUSSION: We demonstrate that mapping of prostate cancer is more than a simple method of documentation but may serve as a method for visual estimation of tumor volume of prostate cancer after radical prostatectomy. This method can further be used for a visual documentation of the tumor stage independent of changes in the TNM classification. The method is inexpensive and practicable and can therefore be applied in routine surgical pathology.

[Use of the S3 guidelines for early detection of prostate cancer in urological practices]. / Anwendung der S3-Leitlinie zur Prostatakrebsfrüherkennung in urologischen Praxen.

OBJECTIVES: The German S3 guideline on prostate cancer gives recommendations on early detection of prostate cancer. In this study we analyzed the adherence of urologists in private practice from the administrative district of Münster, Germany to this guideline. METHODS: Data were collected through a semistructured survey of 22 urologists based on the COREQ checklist (Consolidated criteria for reporting qualitative research) in four focus groups consisting of five or six urologists in private practice. We developed 23 questions relating to 12 recommendations of the paragraphs of the S3 guidelines dealing with early detection of prostate cancer and prostate biopsy. The recommendations of the guideline are subdivided in nine "strong", one "optional recommendation" and two "statements". The adherence to the guideline was investigated by using frequency and qualitative content analysis (Mayring) based on a mixed methods design. RESULTS: The urologists follow six of the nine "strong recommendations" of the guideline and deviate from three. Reasons for deviations from "strong recommendations" are the following: information about advantages and disadvantages of early detection for prostate cancer, recommendation of a prostate biopsy in case of PSA level ≥4 ng/ml, and indication for repeat biopsy. CONCLUSION: Most of the "strong recommendations" are followed by the interviewed urologists of the administrative district of Münster. Contextually relevant deviations from "strong recommendations" are justified, e. g., the only limited transferability of the PSA threshold of 4 ng/ml derived from population-based studies of asymptomatic men to men presenting in a urologist's office.

Isolation of prostate-derived single cells and cell clusters from human peripheral blood.

The detection of blood-borne prostate cancer (PCA) cells may help with clinical staging and the further understanding of PCA metastases. We discovered prostate-specific antigen (PSA)-positive stained but not PSA mRNA-expressing blood cells by means of cell sorting and PSA reverse transcription-PCR in patients. Therefore, we developed a cytokeratin immunomagnetic method to isolate PSA-positive epithelial cells from the circulating blood of PCA patients. We obtained blood-borne single cells from 6 of 10 PCA patients and clustered cells from 8 of 10 PCA patients. Patients with benign prostate hyperplasia tested negative for cell clusters. The reported isolation method yielded prostate-derived cells or clusters of them from PCA-diagnosed patients.

Cytogenetic analysis of multifocal bladder cancer supports a monoclonal origin and intraepithelial spread of tumor cells.

Bladder cancer is often characterized by a multifocal growth pattern. This observation has given rise to the hypothesis of "field cancerization," predicting a polyclonal origin of multiple tumors rising from an area of independently transformed mucosa cells. On the other hand, genetic studies suggested a monoclonal origin. To address these contradictory hypotheses, we performed comparative genomic hybridization (CGH) on 32 tumors originating from six bladder cystectomy specimens. All tumors derived from the same patient showed a set of 7-13 identical chromosomal aberrations and additional individual alterations. Most striking were the findings of 17p losses in all (32 of 32) tumors of the six cystectomy specimens and 20p gains in all tumors of four bladders, as well as an unexpected high number of chromosomal changes (20.4 alterations per tumor on average). To clarify a possible role of the TP53 tumor suppressor gene on 17p13, we applied immunohistochemistry and sequence analysis on the tumors and additional 52 mucosa samples. Identical TP53 mutations and protein overexpression was found in individual tumors only as well as in mucosa samples from continuous areas. Our results not only provide further evidence for a monoclonal origin of multifocal bladder cancer but also point at intraepithelial migration of tumor cells carrying specific chromosomal aberrations.

Patterns of chromosomal imbalances in muscle invasive bladder cancer.

Cytogenetic investigations of bladder cancer suggested that development and progression is characterized by specific chromosomal aberrations. In order to identify genetic changes linked to muscle invasive tumors and metastatic growth we analyzed 67 bladder carcinomas (30 pT1 and 37 pT2-4) by means of comparative genomic hybridization (CGH). The most frequent changes were gains of chromosome 1q (54%), 8q (54%), 17q (49%), 2p (30%), 12 (30%), 5p (25%), 3q (24%) and 6p (24%) as well as losses of 11p (43%), 8p (42%), 9p (36%), 11q (34%), 2q, 4q, 5q (30% each), 9q (27%) and 10q (27%). Previously not described amplifications were found at 5p11-p13, 7q21-q31, 9p24 and 17q24-q25. Gains of 3q, 7p, and 18p were markedly more frequent in pT2-4 in comparison to pT1 carcinomas but the difference did not reach statistical significance. Non-metastatic tumors showed more aberrations on average than metastatic carcinomas, although no particular change was found to be predominating in either group. Our data confirm previous findings of strong genetic similarities between minimally and deeply invasive bladder carcinomas but argue for differences between metastatic and non-metastatic disease.

Generalization of the discriminative stimulus properties of delta 9-THC to delta 9(11)-THC in rats.

Rats were trained in a water maze to discriminate between IP injections of 3 mg/kg delta 9-tetrahydrocannabinol (delta 9-THC) and its vehicle. Both delta 8- and delta 9(11)-THC were generalized to the training drug. In contrast to our observations in rhesus monkeys, where delta 9(11)-THC is at least 100 times less potent than delta 9-THC, delta 9(11)-THC was found to be only seven times less potent in the rat. Relative potencies, expressed as the dosage at which 50% of the animals gave drug responses (ED50) were 1.8 mg/kg and 12.2 mg/kg for delta 9- and delta 9(11)-THC respectively. Twenty-four hours after receiving 7 X ED50 = 12 mg/kg delta 9-THC the tests showed intermediate results when conducted with the training dosage; 4 X ED50 = 50 mg/kg delta 9(11)-THC 48 h prior to the training dosage of 3 mg/kg delta 9-THC completely blocked drug-appropriate responses. Coinjection of ED50 dosages of delta 9- and delta 9(11)-THC led to 90% drug responses, demonstrating the additivity of the cannabis-like effect of both cannabinoids. Differences in the individual sensitivity of the rats to the tested cannabinoids were observed. Findings are interpreted in terms of the receptor mechanism for cannabis-like activity.

Flow cytometric DNA and phenotype analysis in pathology. A meeting report of a symposium at the annual conference of the German Society of Pathology, Kiel, Germany, 6-9 June 2000.

This meeting report summarizes the presentations of three different groups that are active in the field of flow cytometry (FCM) in relation to diagnosing and classification of proliferative disorders. The report starts with the contribution from Regensburg about the developments in DNA FCM, the progression to dual parameter determinations, and combination of immunophenotyping in combination with DNA. In the second part, the use of FCM for the detection of isolated tumor cells in the peripheral blood from patients with prostate or breast cancer is discussed in a contribution from Münster. In the third part, from Heerlen, the use of multi-parameter FCM on formalin-fixed paraffin-embedded tissues from solid tumors is discussed as a new development and application in routine surgical pathology.

Impact of free prostate-specific antigen on discordant measurement results of assays for total prostate-specific antigen.

OBJECTIVES: To determine why various assays for total PSA (t-PSA) produce discordant results in identical serum samples. METHODS: A total of 84 sera from 40 patients with histologically confirmed benign prostatic hyperplasia and from 44 patients with untreated prostate cancer were analyzed with seven assays for t-PSA and the Hybritech research assay for free prostate-specific antigen (f-PSA). Comparison between assays was performed by linear regression of the t-PSA concentrations as well as between the t-PSA concentrations and the f/t-PSA ratios. RESULTS: The coefficients of correlation for the investigated assays versus Hybritech Tandem-E range from 0.96 to 0.99. Nevertheless average PSA concentrations differed significantly from the Tandem-E assay in all assays. Despite a good correlation, some assays showed a regression line with a slope notably different from 1. In these assays, elevated concentrations were observed in sera with a high proportion of f-PSA. CONCLUSIONS: The study illustrates a significant and clinically relevant discordance between reported t-PSA concentrations for identical samples, depending on the assay used and on the contents of f-PSA in the sample. The interpretation of t-PSA concentrations requires awareness of the applied assay as well as the establishment of an assay-specific reference range in order to avoid inappropriate clinical consequences, such as unnecessary biopsies. Respective details must be contained in the laboratory reports. A change of assays without specifically reassessing previously valid reference ranges or the uncritical use of a customarily applied limit of < 4 ng/mL will otherwise be harmful to the patient.

Estradiol and high-dose dihydrotestosterone treatment causes changes in cynomolgus monkey prostate volume and histology identical to those caused by testosterone alone.

To evaluate the effects of testosterone (T), dihydrotestosterone (DHT), and estradiol (E2) on the regulation of prostate growth and tissue composition, the following study was conducted in a nonhuman primate model. Fifteen adult, long-term castrated cynomolgus monkeys were randomly assigned to receive implants filled with T (0.19 +/- 0.01 g), DHT alone (0.21 +/- 0.01 g), or (99%) DHT + (1%) E2 (0.21 +/- 0.01 g). Prior to and at 4-week intervals during the treatment phase of 252 days, prostate volumes (PV), body weight, ejaculate weight, hormone levels (of T, DHT, and E2), and red blood cell count were measured. Five adult, intact monkeys served as controls for prostate volume and histology. At the end of the study, histological analysis of an ultrasound-guided prostate biopsy was performed. T levels increased significantly in the T group compared with baseline (P < 0.01) and with the DHT and DHT + E2 groups (P < 0.05). Both groups receiving DHT showed higher DHT levels than did animals in the T group (P < 0.001). E2 levels in all groups increased over time (P < 0.05), although significant differences (P < 0.01) could only be detected between the DHT + E2 and the DHT group. Prostate volume in all groups increased (at baseline: T = 1.03 +/- 0.12 ml, DHT = 1.08 +/- 0.15 ml, DHT + E2 = 1.13 +/- 0.09; at day 252: T = 5.83 +/- 1.00, DHT = 4.72 +/- 0.9, DHT + E2 = 5.05 +/- 0.62) over time (P < 0.001), whereas no differences could be detected between the groups. Prostate biopsy could be performed successfully in 15 out of 20 monkeys. Prostate tissue evaluation between the treatment groups and the evaluated intact monkeys revealed no differences in the status of secretory epithelia, nuclear chromatin, excretory vacuoles, interstitial stroma, smooth muscles, and total functional status, whereas the prostate of a long-term castrated monkey showed severe atrophy. Thus, both androgens fully restored prostate volume and ejaculatory function. Highly supraphysiological DHT serum levels are not associated with abnormal volumetric or histological changes of the prostate. Comparing the DHT group with the DHT + E2 group, an additional stimulatory effect of normal or slightly elevated estrogens on the prostate cannot be found in the presence of highly supraphysiological DHT levels.

Radical prostatectomy: survival outcome and correlation to prostate-specific antigen levels.

BACKGROUND: This paper reviews a 10-year experience with radical retropubic prostatectomy (RP) focussing on survival outcome related to pre- and postoperative levels of prostate-specific antigen (PSA). PATIENTS AND METHODS: 739 patients who underwent RP between 1987 and 1998 were prospectively investigated. Kaplan-Meier analyses were performed and correlated to pre- and postoperative PSA concentrations. RESULTS: In a follow up period of 11 years duration, (mean 3 yrs.) 57 of 739 patients died (20 from prostate disease progression, 37 from other causes). Correlation between low pre-operative PSA and pathological organ-confinement was significant (p < 0.001). Of 175 patients with PSA progression, 53 (30%) had never reached undetectable levels of PSA. 57% of PSA relapses were detected during the first year, and 3% later than 5 years post-operatively. Kaplan-Meier analysis yielded an average 3 years advantage in estimated prostate-cancer-specific survival when pre-operative PSA levels were below 50 ng/ml. Overall, prostate-cancer-specific and PSA-free 5-year survival-rates were 88%, 96% and 67% respectively. CONCLUSIONS: Survival-rates after RP are high even in conjunction with unfavourable PSA outcome. Merely one third of deaths resulted from prostate cancer, since men at risk frequently suffer from concomitant diseases that affect survival.

Prostate specific antigen in as a dynamic model in advanced prostate cancer.

BACKGROUND: Prostate specific antigen doubling time (PSADT) is a prognostic factor after radical prostatectomy, radiation therapy, and hormonal therapy respectively for prostate cancer. However, its role in patients receiving chemotherapy has not been evaluated to date. PATIENTS AND METHODS: Thirty patients (pts.) with hormone resistant prostate cancer were enrolled in a prospective phase II study to receive oral Idarubicin. The drug was administered at a dose of 35 mg on day 1 and 8 of each cycle, and treatment was repeated every 3 weeks. RESULTS: Fully evaluable for response were 26 pts. 13 of these 26 had measurable disease and 3 out of 13 had no change (NC) after therapy. Ten pts. had progression. All 13 pts. with non-measurable disease showed no response. PSA values increased exponentially over time in all pts., except for the 3 pts. with NC, in whom PSA values remained stable. Median PSADT of pts. with a rising PSA was 2.1 months (mean 2.6; range 0.7-6.1). CONCLUSIONS: PSA levels in pts. not responding to treatment with Idarubicin rose in an exponential fashion similar to pts. who were only on hormonal therapy. PSADT should be evaluated in a larger number of hormone resistant prostate cancer pts. as a possible surrogate endpoint.

The biologic lower detection limit of six ultrasensitive PSA assays.

BACKGROUND: The benefit of monitoring patients with prostate cancer (PCA) by ultrasensitive measurement of prostate specific antigen (PSA) is frequently discussed. Usually, the analytic lower detection limit of an ultrasensitive assay is determined by the manufacturer. As the analytic lower detection limit does not take into account interfering factors of human serum, the biologic lower detection limit, which is defined as PSA concentration detected in PSA-free human serum, plus 3 standard deviations, is of greater interest. MATERIALS AND METHODS: We investigated the biologic lower detection limit of six ultrasensitive PSA assays. Sera from 15 men with bladder cancer after radical cystoprostatectomy and from 30 healthy women were applied. Hence, we expected no PSA of prostatic origin. RESULTS: The biologic lower detection limit obtained using these sera was up to 30 fold higher (men, 0.29-0.63 ng/ml; women, 0.03-0.69 ng/ml) than the analytic lower detection limit (0.01-0.09 ng/ml). CONCLUSIONS: PSA measurement in sera obtained from men without prostate and women results in PSA values above the ultrasensitive range. Therefore, advantages provided by ultrasensitive PSA measurement in monitoring PCA patients after radical prostatectomy are limited.

The use of prostate-specific antigen (PSA) for the monitoring of radiation therapy in prostate cancer.

BACKGROUND: The classic methods for surveilling the efficacy of radiotherapy in prostate cancer are not accurate enough. The objective of this analysis was to determine whether prostate-specific antigen could perform this task. MATERIALS AND METHODS: From 1/95 to 10/95, 16 patients were treated at our clinic. 7 of these underwent primary irradiation, 4 treatment for local recurrence, and 5 had adjuvant radiotherapy. Radiotherapy was carried out with a total dose of 60 Gy in 30 fractions, 10 fractions per week, to the prostate bed plus 2 cm safety margin. RESULTS: PSA levels usually start to decline between the 3rd and the 4th week of radiotherapy with a half-life of 2.5 months. Five patients had equal or rising PSA levels, including all three patients with recurrent tumor. DISCUSSION: In most cases, PSA declined continuously from the 3rd week of therapy. Our median half-life was similar to other reported results. Persisting or rising PSA levels are an indicator for local or distant recurrence; all our patients who developed a recurrence showed a corresponding PSA increase.

Elimination kinetics of prostate-specific antigen serum and urine.

The serum half-life of prostate-specific antigen (PSA) was calculated in 66 patients subsequent to radical prostatectomy. Comparing serum half-life to disease outcome in 37 patients after a minimum follow-up of two years, it was found that PSA serum half-life identifies patients with residual disease earlier and more reliably than the presence or absence of detectable PSA levels postoperatively. It is suggested that residual tumor affects the half-life by contributing to the serum level of PSA. When PSA serum half-life was calculated solely in potentially cured patients, we found a half-life of 1.6 days, which is considerably shorter than in previous reports based on patient populations regardless of the outcome of disease in the follow-up. To elucidate the route of PSA elimination, serial urine PSA levels were determined before and after radical prostatectomy, revealing strong evidence for the assumption that PSA is not eliminated by the kidneys in its unchanged form.

Blood-borne cancer cells--quo vadis?

The detection of blood-borne cancer cells may help in clinical staging and further understanding of cancer metastasis. We developed a cytokeratin-based immunomagnetic method to isolate epithelium-derived cells from the circulating blood of patients. The number of cell clusters positive for cytokeratin/prostate-specific antigen (PSA) from the peripheral blood of prostate cancer patients and cytokeratin/p185c-erbB-2 from the peripheral blood of breast cancer patients has been related to stage of the disease. Breast cancer patients who presented cytokeratin/p185c-erbB-2-positive cell clusters showed a decrease in such cells under adriamycin adjuvant therapy with Further molecular characterization by a highly sensitive microsatellite multiplex-PCR enabled reproducible detection of microsatellite alterations. The impact of these individually targeted results may contribute to an individual diagnostic and therapeutic strategy.

The impact of intraoperative manipulation of the prostate on total and free prostate-specific antigen.

OBJECTIVES: It is well documented that mechanical manipulation of the prostate can elevate total PSA (t-PSA) levels in serum. However, less is known about its effects on free PSA (f-PSA) and the free-to-total PSA ratio (f/t-PSA). We therefore examined the impact of prostate manipulation on t-PSA and f-PSA during surgical procedures involving the prostate. METHODS: Intraoperative blood samples for t-PSA and f-PSA measurement (Hybritech) were collected every 15 min during 14 radical retropubic prostatectomies (RRP) and 10 radical cystoprostatectomies (RCP). RESULTS: Prostatic manipulation induced significant elevations in t-PSA and f-PSA during RRP and RCP. Postmanipulatory peaks were markedly higher for f-PSA than for t-PSA. The mean maximum f-PSA levels showed a 4.3- (RRP) and 7.9-fold (RCP) increase, followed by a rapid decline after prostate removal. t-PSA increased 1.2- (RRP) and 1.3-fold (RCP), and declined more slowly. Postmanipulatory f/t-PSA ratios also increased significantly, reaching mean elevations of +0.29 and +0.28 over preoperative ratios during RRP and RCP, respectively. CONCLUSIONS: Prostate manipulation can induce transient increases in t-PSA, f-PSA and f/t-PSA in benign and malignant prostates. The extent of these alterations and their course over time must be taken into account when postmanipulatory changes in PSA forms are investigated. Timing of postmanipulatory venipunctures and the molar response ratio of t-PSA assays used (equimolar versus nonequimolar) seem to have substantial impact on the results of such studies.

Frequent detection and immunophenotyping of prostate-derived cell clusters in the peripheral blood of prostate cancer patients.

BACKGROUND: Recent scientific studies have failed to determine parameters for the assessment of prostate cancer aggressiveness. The present study deals with the detection of blood-borne cancer cells based on polymerase chain reaction (PCR) and cell enrichment methods. The contradictory results reported in the literature have called into question the clinical usefulness of this diagnostic method in the preoperative staging of clinically localized prostate cancer. METHODS: We established a combined method of density gradient centrifugation and immunomagnetic separation using epithelium-specific antibodies, i.e. cytokeratins, to isolate prostate-derived circulating cells from the peripheral blood of patients with prostate cancer. Isolated cells were characterized by DNA staining and immunocytochemistry using antibodies for the detection of prostate-specific antigen (PSA), proliferation-associated proteins (MIB-1, H1 and H3) and apoptosis-associated proteins (M30, c-FasR). RESULTS: We applied these methods to 68 prostate cancer patients and were able to isolate cell clusters in 98%. Immunophenotypic and morphological characterization of PSA-positive prostate-derived cell clusters found in the peripheral blood of prostate cancer patients showed two main populations: 1) in 35% of the investigated prostate cancer patients we detected rounded cell aggregates of probable cancer cells expressing proliferation-associated proteins and lacking apoptosis-associated protein expression; 2) in all cases there was a high frequency of circulating dysmorphic cell clusters positive for apoptosis-associated protein expression. CONCLUSION: Our results demonstrate the existence of at least two different types of blood-borne prostate-derived circulating cell clusters. Of these, only the less frequent, round, small cell clusters harbor features that are probably necessary for the cells to survive for metastatic spread.