Physiological variation of serum prostate specific antigen in the 4.0 to 10.0 ng./ml. range in male volunteers

PURPOSE

Because some patients show a surprising variation in serial serum prostate specific antigen (PSA) values, we determined the intra-individual or physiological variation in serum PSA by collecting sera 2 to 3 week apart without any prostatic manipulation.

MATERIALS AND METHODS

Because 4.0 to 10.0 ng./ml. PSA is the critical range for decision making, we asked all men with a PSA in this range to return 2 to 3 weeks later for a second measurement. Total serum PSA was determined by the Hybritech Tandem-R, automated Tosoh AIA-600 and Delfia section immunoassays. Free and complexed serum PSA was determined by the Delfia assays. Between assay variation (first blood specimen retested on a separate day with the second blood specimen) was compared to the physiological variation (first versus second blood specimens).

RESULTS

Mean coefficient of variation (95% confidence limits) was 10.5% for between assay and 23.5% for physiological evaluations. The preferred analysis of ratio difference variation provided a factor of 0.138 (between assay) and 0.298 (physiological) for 95% confidence limits. Changes in free or complexed PSA were not the cause of physiological variation.

CONCLUSIONS

The intra-individual physiological variation is 2 to 3 times the between assay variation for sera drawn 2 to 3 weeks apart with a PSA of 4 to 10 ng./ml. A serum PSA of 4.0 ng./ml. can increase to 5.2 ng./ml. (4.0 x 0.298) and still be within the physiological variability for 95% confidence limits.

Effect of flutamide and flutamide plus castration on prostate size in patients with previously untreated prostate cancer

OBJECTIVES

Transrectal ultrasonography (TRUS) was used in previously untreated men with prostate cancer undergoing hormonal therapy to provide objective observations on the decrease in prostate size and to assess the usefulness of prostate size in estimating treatment response.

METHODS

In this retrospective study, 31 patients with previously untreated prostate cancer (Stage T1c to D2) who received hormonal therapy (flutamide, n = 18; flutamide plus castration, n = 13) were followed with serial estimations of prostate size by TRUS and by serum prostate-specific antigen (PSA).

RESULTS

In both treatment groups, the major decreases in prostate size were noted within the first 6 months of therapy, whereas further follow-up examinations failed to show statistically significant changes. Prostate size decreased by 48% in men treated with flutamide, whereas those treated with flutamide plus castration showed a statistically significant greater decrease, mean of 56% (P < or = 0.01). Six patients (33%) in the flutamide group and 5 (38%) men in the total androgen deprivation group ultimately failed therapy as indicated by a rising PSA level. Only 55% (n = 6) of the patients who progressed showed an increase in prostate size.

CONCLUSIONS

Total androgen deprivation in comparison to flutamide alone caused a larger reduction in prostate size. As a marker of hormonal failure, a rising PSA was more sensitive than an increase in prostate size.

The periurethral glands do not significantly influence the serum prostate specific antigen concentration

PURPOSE

The periurethral glands are known to produce prostate specific antigen (PSA). With ultra-sensitive assays now routinely available, it is necessary to determine if the periurethral glands significantly influence serum PSA concentration after radical prostatectomy.

MATERIALS AND METHODS

Serum PSA levels of 46 men, 51 to 89 years old (median age 67) who underwent radical cystoprostatectomy and total urethrectomy, were compared with those of 92 men 46 to 91 years old (median age 67) who underwent radical cystoprostatectomy only. All men had transitional cell carcinoma of the bladder without gross or microscopic evidence of prostate cancer and all underwent ileal conduit diversion. Serum was obtained at least 1 year postoperatively. Each specimen was analyzed using the Tosoh, Immulite, and Yu and Diamandis ultra-sensitive PSA assays with analytical detection limits of 0.02 ng./ml., 0.004 ng./ ml. and 0.002 ng./ml., respectively.

RESULTS

Median PSA for the radical cystoprostatectomy with urethrectomy group was 0.00 ng./ml. (range 0.00 to 0.14) for each of the 3 assays. For the radical cystoprostatectomy only group the median Tosoh and Immulite PSA assay levels were 0.01 ng./ml. (range 0.00 to 0.22), and median Yu and Diamandis PSA assay level was 0.00 ng./ml. (range 0.00 to 0.31).

CONCLUSIONS

The greatest difference in median PSA levels that could be found between men with and without periurethral glands when using 3 different ultra-sensitive assays was 0.01 ng./ml., indicating that the periurethral glands do not have a clinically significant effect on serum PSA concentration after radical prostatectomy. Thus, a serum PSA level above the residual cancer detection limit following radical prostatectomy, even if obtained with a ultra-sensitive assay, reflects either malignant or benign residual prostatic tissue, rather than the presence of periurethral glands.

Physiologic (intraindividual) variation of serum prostate-specific antigen in 814 men from a screening population

OBJECTIVES

We measured the intraindividual variation of prostate-specific antigen (PSA) in the serum of healthy men screened for prostate cancer.

METHODS

We used a fully automated PSA assay system (ACS: 180 assay) to evaluate a screening population of 814 men (mean age, 63.3 years; range, 50 to 79 years) without documented prostate cancer or prostate surgery. A second blood sample was drawn 15 to 183 days after the first specimen (mean, 80 days).

RESULTS

In the ACS PSA ranges of 0 to 7.2 ng/mL, 7.3 to 17.9 ng/mL, and 18.0 ng/mL or greater (O to 4 ng/mL, 4 to 10 ng/mL, and 10.0 ng/mL or greater by the Tandem-R assay), the mean coefficient of variation of the first and second blood drawn was 20%, 12%, and 10%, respectively. In 435 men whose first blood samples were measured twice for PSA difference (interassay or run-to-run variation), the intraindividual variation in the range of 0 to 7.2 ng/mL was significantly larger than the interassay variation, which was also true the 7.3 to 17.9 ng/mL range. In the range of 0 to 7.2 ng/mL, 251 of 695 (36%) showed a 20% or greater relative increase and 69 of 695 (10%) showed a 1.3 ng/mL (0.75 ng/mL by the Tandem-R assay) or greater absolute increase of PSA at the second blood sample.

CONCLUSIONS

We conclude that in the low ranges of PSA concentrations, one should consider the possibility of substantial intraindividual variation when interpreting serial PSA measurements.

RS-17053 (N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro-alpha, alpha-dimethyl-1H-indole-3-ethanamine hydrochloride), a selective alpha 1A-adrenoceptor antagonist, displays low affinity for functional alpha 1-adrenoceptors in human prostate: implications for adrenoceptor classification

Norepinephrine (NE) contracts smooth muscle cells within the human lower urinary tract (LUT) (bladder neck, prostate, and urethra). Receptor distribution and pharmacological evidence have implicated activation of alpha 1A-adrenoceptors. We disclose the pharmacological properties of the novel, selective alpha 1A-adrenoceptor antagonist N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro- alpha,alpha-dimethyl-1H-indole-3-ethanamine hydrochloride (RS-17053) and examine critically the pharmacological identity of the alpha 1-adrenoceptor mediating contractions to NE in human LUT tissues. In several tissues from rat and cloned adrenoceptors, RS-17053 displayed high affinity for the alpha 1A-adrenoceptor (pKi and pA2 estimates of 9.1-9.9) and a 30-100-fold selectivity over the alpha 1B- and the alpha 1D-adrenoceptor subtypes (pK1 and pA2 estimates of 7.7-7.8). However, in isolated smooth muscle preparations from human LUT tissues, RS-17053 antagonized responses to NE only at high concentrations. Estimates of affinity (pA2) at alpha 1-adrenoceptors mediating NE-induced contractions were 7.5 in prostatic periurethral longitudinal smooth muscle (compared with 8.6 for prazosin), 6.9 in anterior fibromuscular stroma (prazosin, 8.9), and 7.1 in bladder neck (prazosin, 8.5). These findings indicate that contractile responses to NE in human LUT tissues are mediated by a receptor displaying pharmacological properties that are clearly different from those of the defined alpha 1A-adrenoceptor and raise the possibility that multiple forms of the alpha 1A-adrenoceptor may exist in human LUT that are discriminated by RS-17053. In this regard, the affinity estimates obtained with RS-17053 and other alpha 1-adrenoceptor antagonists in human LUT tissues are identical to those described for the putative alpha 1L-adrenoceptor.

Histological characteristics of radical prostatectomy specimens in men with a serum prostate specific antigen of 4 ng./ml or less

PURPOSE

Of most reported radical prostatectomy series 20% consist of men with a serum prostate specific antigen (PSA) of 4.0 ng./ml. or less. Since our series is not only prospective but all prostates are reconstructed at 3 mm. intervals, we determined the clinical and histological findings in this important subset of men undergoing radical prostatectomy.

MATERIALS AND METHODS

Of 911 consecutive men undergoing radical prostatectomy 187 (21%) had a preoperative serum PSA of 4.0 ng./ml. or less (values equivalent to those of the Hybritech Tandem-R assay).

RESULTS

Mean tumor volume was 2.3 cc. Of the 187 cancers 156 (83%) were in the peripheral zone and 31 (17%) in the transition zone, while 137 (73%) were organ-confined and 50 (27%) showed capsular penetration. No patient had positive pelvic lymph nodes, only 5 had seminal vesicle invasion and positive surgical margins were present in 14%. Cancer volumes less than 0.5 cc were noted in 9% of the patients and were probably insignificant. At an average followup of 37 months, only 16 men (9%) had a detectable serum PSA. These 16 patients had a larger tumor volume (3.7 cc versus 2.2 cc, p < 0.05), and a greater percent of Gleason grade 4 and/or 5 disease than the 171 with undetectable PSA.

CONCLUSIONS

Men with prostate cancer and a serum PSA of 4.0 ng./ml. or less are excellent candidates for radical prostatectomy if the 9% with clinically insignificant tumors can be avoided. Since 70% of all men had a suspicious prostate on digital rectal examination, this evaluation is important for men with a serum PSA of 4.0 ng./ml. or less.

Limitations of serum prostate specific antigen in predicting peripheral and transition zone cancer volumes as measured by correlation coefficients

PURPOSE

We reexamined the relationship between preoperative serum prostate specific antigen (PSA) and prostate cancer volume in 290 patients who underwent radical prostatectomy.

MATERIALS AND METHODS

Serum samples from 290 consecutive patients were remeasured with the automated monoclonal-monoclonal Tosoh AIA-600 assay. These values were correlated with individual cancer volume by measuring Pearson correlation coefficients (r).

RESULTS

Cancer was noted in the transition zone in 31 patients and in the peripheral zone in 259. Of the peripheral zone cancers 133 (51.4%) were organ confined and 126 (48.6%) were nonorgan confined, including 12 (9.5%) with histologically confirmed lymph node metastasis (stage D1). The 259 peripheral zone cancers had a correlation coefficient with PSA (r = 0.499, p < 0.0001). After distributing the 259 cases into cancer volume groups we found a large overlap in mean preoperative serum PSA, including 65 with 50% or greater Gleason grade 4 or 5 disease (r = 0.508). The correlation coefficients of cancer volume with PSA in 133 organ confined cancers, 114 nonorgan confined cancers without lymph node metastases and 12 nonorgan confined cancers with positive lymph nodes were 0.382, 0.438 and 0.363, respectively. The 31 transition zone cancers showed a correlation coefficient with PSA (r = 0.81). After excluding 2 cases with extreme PSA and cancer volume the correlation coefficient decreased (r = 0.077).

CONCLUSIONS

Even when remeasured with an automated monoclonal-monoclonal assay serum PSA alone is unable to predict preoperatively cancer volume or distinguish between organ and nonorgan confined cancer in peripheral and transition zone tumors of the prostate.

Identity of PSA purified from seminal fluid by different methods: comparison by amino acid analysis and assigned extinction coefficients

To determine the true extinction coefficient of prostate specific antigen (PSA) and to measure any differences in PSA when isolated from seminal fluid by four different published methods, we studied 10 different lots of PSA by quantitative amino acid analysis. Despite an expected PSA concentration of 1 mg/ml based on gravimetric analysis at an average optical density of 1.45 at 280 nm, we recovered only 0.79 mg/ml by quantitative amino acid analysis (range 0.752 to 0.820 mg/ml with a coefficient of variation [C.V.] of 3.3% among the 10 lots). The concentration of 0.79 mg/ml was based on a molecular weight of 28,430 daltons for glycosylated PSA determined by ion spray mass spectroscopy [Bélanger et al: Prostate, 27:187-197, 1995]. From these 10 amino acid analyses, we calculated the extinction coefficient of PSA at 280 nm as 1.84 +/- 0.04 ml x mg-1 x cm-1 (range 1.78 to 1.90 with a C.V. of 2.2%). Similar concentrations of PSA were obtained by amino acid analysis regardless of the method of purification. These observations support the presence of a single form of PSA in seminal fluid and are consistent with the molecular evidence that PSA is transcribed from a single gene locus on the long arm of chromosome 19 [Riegman et al.: Genomics 14:6-11, 1992]. They do not support the recent contention by the Roswell Park group that the PSA they isolated in 1979 [Wang et al.: Invest Urol 17:159-163, 1979; Wang et al.: Prostate 24:107-108, 1994] is different from p30 reported a year earlier [Sensabaugh: J Forensic Sci 23:106-115, 1978].

Molecular mass and carbohydrate structure of prostate specific antigen: studies for establishment of an international PSA standard

Despite the widely accepted use of prostate specific antigen (PSA) as a marker of prostate cancer, this molecule has not yet been completely characterized. Past studies have well established, however, using both amino acid and cDNA sequencing techniques, that PSA contains 237 amino acids, with a molecular mass of 26,079 Da for the peptide moiety of the molecule. The present study reports analysis of this protein by ion spray mass spectrometry (ISMS) and analysis of its carbohydrate moiety by NMR spectroscopy. The predominant PSA molecular species detected by ISMS was at relative molecular mass (M(r)) of 28,430, indicating that PSA contains a carbohydrate residue of M(r) 2,351, for a total percentage of carbohydrate of 8.3%. Analysis of PSA by SDS-PAGE, however, showed a M(r) of 32,000 to 33,000, suggesting an overestimation of the molecular weight by the latter technique. The complete primary structure of the PSA carbohydrate chain was determined by NMR spectroscopy in combination with carbohydrate composition analysis. The experimentally determined carbohydrate content of PSA confirms that only one N-glycosylation site is occupied in the protein. The proposed carbohydrate structure is a diantennary N-linked oligosaccharide of the N-acetyllactosamine type, with a sialic acid group at the end of each of the two branches. In addition, our data indicate that approximately 70% of the PSA molecules contain a fucose group in the core chitobiose moiety. The calculated molecular weight of this carbohydrate structure (M(r) 2,351.8) is in excellent agreement with the predicted molecular weight of the carbohydrate group, based on the M(r) 28,430 for PSA measured by ion spray mass spectrometry and M(r) 26,079 calculated from the consensus sequence for the peptide portion of the molecule. ISMS of PSA is thus proposed as a convenient and reliable method of quality control, an indispensible step towards international standardization of this very important tumor marker for detection and monitoring of prostatic diseases, especially prostate cancer.

Purification and characterization of prostate-specific antigen (PSA) complexed to alpha 1-antichymotrypsin: potential reference material for international standardization of PSA immunoassays

We describe for the first time a protocol to purify to apparent homogeneity an in vitro-prepared complex of prostate-specific antigen (PSA) and alpha 1-antichymotrypsin (ACT) by using a combination of gel filtration and ion-exchange chromatography. The purity of the PSA-ACT complex was confirmed by gel electrophoresis and Western blot. The PSA-ACT complex was stable in the pH range 6.0 to 7.8; it was also stable in various matrices, temperatures, and high concentrations of salt. Purification of the PSA-ACT complex was highly reproducible. An absorptivity of 0.99 L x g-1 x cm-1 at 280 nm was assigned to the PSA-ACT complex, based on amino acid analysis. Because PSA and ACT bind in a 1:1 molar ratio, we determined the molecular mass of the PSA-ACT complex as the mass encoded by the cDNA of ACT (plus 26% carbohydrate) plus the molecular mass of PSA (28,430 Da), which totals 89,280 Da. Using this material, we made two common calibrators, one of 100% PSA-ACT complex and one of 90% PSA-ACT complex plus 10% free PSA by volume (90:10 calibrator). Substitution of these calibrators for the manufacturers' calibrators in nine commercial immunoassays substantially reduced differences between immunoassays, especially for serum PSA values between 4 and 10 micrograms/L. The 90:10 calibrator is recommended as a universal calibrator for international standardization of PSA immunoassays.

Interpretation of bilateral positive biopsies in prostate cancer

PURPOSE

When 6 systematic prostate needle core biopsies are positive for cancer bilaterally, prediction of clinical cancer volume is limited by the unpredictable presence of contralateral incidental tumors. Criteria were sought to improve prediction.

MATERIALS AND METHODS

Core cancer lengths were summed unilaterally (3 biopsies) and bilaterally (6) in 65 patients with bilateral positive cores. Of the patients 31 had true bilateral cancer spread and 34 had unilateral disease with contralateral incidental tumors.

RESULTS

For both groups correlation with prostatectomy cancer volume (r = 0.65, p < 0.001) was the same for the sum of 3 ipsilateral cores as for all 6 cores.

CONCLUSIONS

Core cancer length sum of 3 ipsilateral biopsies predicts the largest prostatectomy cancer volume as well as the bilateral sum. Contralateral biopsies do not contribute to prediction nor distinguish bilateral spread from contralateral incidental cancers.

Purification and characterization of prostate-specific antigen (PSA) complexed to alpha 1-antichymotrypsin: potential reference material for international standardization of PSA immunoassays

We describe for the first time a protocol to purify to apparent homogeneity an in vitro-prepared complex of prostate-specific antigen (PSA) and alpha 1-antichymotrypsin (ACT) by using a combination of gel filtration and ion-exchange chromatography. The purity of the PSA-ACT complex was confirmed by gel electrophoresis and Western blot. The PSA-ACT complex was stable in the pH range 6.0 to 7.8; it was also stable in various matrices, temperatures, and high concentrations of salt. Purification of the PSA-ACT complex was highly reproducible. An absorptivity of 0.99 L x g-1 x cm-1 at 280 nm was assigned to the PSA-ACT complex, based on amino acid analysis. Because PSA and ACT bind in a 1:1 molar ratio, we determined the molecular mass of the PSA-ACT complex as the mass encoded by the cDNA of ACT (plus 26% carbohydrate) plus the molecular mass of PSA (28,430 Da), which totals 89,280 Da. Using this material, we made two common calibrators, one of 100% PSA-ACT complex and one of 90% PSA-ACT complex plus 10% free PSA by volume (90:10 calibrator). Substitution of these calibrators for the manufacturers' calibrators in nine commercial immunoassays substantially reduced differences between immunoassays, especially for serum PSA values between 4 and 10 micrograms/L. The 90:10 calibrator is recommended as a universal calibrator for international standardization of PSA immunoassays.

Nerve sparing radical prostatectomy: a different view

Erectile dysfunction was evaluated in 459 men with prostate cancer before and after radical prostatectomy. Potency was defined as the ability to achieve unassisted intercourse with vaginal penetration. Of the patients 51 were potent postoperatively, including 2 of 187 (1.1%) undergoing surgery without nerve sparing, and 27 of 203 (13.3%) undergoing unilateral and 22 of 69 (31.9%) undergoing bilateral nerve sparing prostatectomy. Less than half of the patients who were sexually active postoperatively were satisfied with the erections or achieved intercourse at least once a month. Postoperative potency was statistically related to the number of neurovascular bundles spared, frequency of intercourse preoperatively, absence of seminal vesicle or lymph node involvement with cancer, absence of postoperative incontinence or strictures, patient age and cancer volume.