Clearance of serum PSA after open surgery for benign prostatic hypertrophy, radical cystectomy, and radical prostatectomy

A critical review of the analytical approaches for circulating tumor biomarker kinetics during treatment

Changes in serum tumor biomarkers may indicate treatment efficacy. Traditional tumor markers may soon be replaced by novel serum biomarkers, such as circulating tumor cells (CTCs) or circulating tumor nucleic acids. Given their promising predictive values, studies of their kinetics are warranted. Many methodologies meant to assess kinetics of traditional marker kinetics during anticancer treatment have been reported. Here, we review the methodologies, the advantages and the limitations of the analytical approaches reported in the literature. Strategies based on a single time point were first used (baseline value, normalization, nadir, threshold at a time t), followed by approaches based on two or more time points [half-life (HL), percentage decrease, time-to-events…]. Heterogeneities in methodologies and lack of consideration of inter- and intra-individual variability may account for the inconsistencies and the poor utility in routine. More recently, strategies based on a population kinetics approach and mathematical modeling have been reported. The identification of equations describing individual kinetic profiles of biomarkers may be an alternative strategy despite its complexity and higher number of necessary measurements. Validation studies are required. Efforts should be made to standardize biomarker kinetic analysis methodologies to ensure the optimized development of novel serum biomarkers and avoid the pitfalls of traditional markers.

Prognostic value of modeled PSA clearance on biochemical relapse free survival after radical prostatectomy

PURPOSES

Using population kinetic approach, we modeled PSA decline equations in patients with prostate cancer after radical prostatectomy (RP). We looked for relationships between early PSA decrease profile, characterized by PSA clearance (CL(PSA)) or half-life (HL(PSA)), and the 2-year biochemical relapse free survival (bRFS).

PATIENTS AND METHODS

We performed a retrospective study on 55 patients treated with RP and with at least 2 PSA measurements in the post-operative month. A population kinetic model was investigated with NONMEM. The prognostic factors regarding bRFS were assessed using univariate and multivariate analyses.

RESULTS

The best model describing the PSA post-operative decrease was bi-compartmental and fit patient data well. Median CL(PSA) was 0.034 (terciles were 0.023 and 0.048). The significant prognostic factors associated with a better bRFS with univariate analysis were lower CL(PSA) terciles (2-year bRFS = 100% vs. 85.1% vs. 66.7% if CL(PSA) < 0.023, 0.023 <or= CL(PSA) < 0.048 or CL(PSA) >or= 0.0480, P = 0.006) as well as initial PSA < 7 ng/ml, pT2 stage (vs. pT3), pN0 (vs. pN1) and low main Gleason score (3/5 vs. 4/5). Among these factors, CL(PSA) was the only independent prognostic factor with multivariate analysis regarding bRFS (HR = 0.92, 95%CI = [0.86-0.98], P = 0.0088).

CONCLUSION

CL(PSA) determined with 4 PSA concentrations in the first month following the RP may predict the biochemical relapse risk of prostate cancer patients, thus enabling early identification of high-risk patients requiring adjuvant treatment. A prospective validation of these results is required.

Cancer screening: a mathematical model relating secreted blood biomarker levels to tumor sizes

BACKGROUND

Increasing efforts and financial resources are being invested in early cancer detection research. Blood assays detecting tumor biomarkers promise noninvasive and financially reasonable screening for early cancer with high potential of positive impact on patients' survival and quality of life. For novel tumor biomarkers, the actual tumor detection limits are usually unknown and there have been no studies exploring the tumor burden detection limits of blood tumor biomarkers using mathematical models. Therefore, the purpose of this study was to develop a mathematical model relating blood biomarker levels to tumor burden.

METHODS AND FINDINGS

Using a linear one-compartment model, the steady state between tumor biomarker secretion into and removal out of the intravascular space was calculated. Two conditions were assumed: (1) the compartment (plasma) is well-mixed and kinetically homogenous; (2) the tumor biomarker consists of a protein that is secreted by tumor cells into the extracellular fluid compartment, and a certain percentage of the secreted protein enters the intravascular space at a continuous rate. The model was applied to two pathophysiologic conditions: tumor biomarker is secreted (1) exclusively by the tumor cells or (2) by both tumor cells and healthy normal cells. To test the model, a sensitivity analysis was performed assuming variable conditions of the model parameters. The model parameters were primed on the basis of literature data for two established and well-studied tumor biomarkers (CA125 and prostate-specific antigen [PSA]). Assuming biomarker secretion by tumor cells only and 10% of the secreted tumor biomarker reaching the plasma, the calculated minimally detectable tumor sizes ranged between 0.11 mm(3) and 3,610.14 mm(3) for CA125 and between 0.21 mm(3) and 131.51 mm(3) for PSA. When biomarker secretion by healthy cells and tumor cells was assumed, the calculated tumor sizes leading to positive test results ranged between 116.7 mm(3) and 1.52 x 10(6) mm(3) for CA125 and between 27 mm(3) and 3.45 x 10(5) mm(3) for PSA. One of the limitations of the study is the absence of quantitative data available in the literature on the secreted tumor biomarker amount per cancer cell in intact whole body animal tumor models or in cancer patients. Additionally, the fraction of secreted tumor biomarkers actually reaching the plasma is unknown. Therefore, we used data from published cell culture experiments to estimate tumor cell biomarker secretion rates and assumed a wide range of secretion rates to account for their potential changes due to field effects of the tumor environment.

CONCLUSIONS

This study introduced a linear one-compartment mathematical model that allows estimation of minimal detectable tumor sizes based on blood tumor biomarker assays. Assuming physiological data on CA125 and PSA from the literature, the model predicted detection limits of tumors that were in qualitative agreement with the actual clinical performance of both biomarkers. The model may be helpful in future estimation of minimal detectable tumor sizes for novel proteomic biomarker assays if sufficient physiologic data for the biomarker are available. The model may address the potential and limitations of tumor biomarkers, help prioritize biomarkers, and guide investments into early cancer detection research efforts.

Total and free PSA kinetics in patients without prostate cancer undergoing radical cystoprostatectomy

BACKGROUND

Radical cystoprostatectomy and radical prostatectomy are the two major operations where prostate is totally and radically removed. Radical cystoprostatectomy is usually performed in patients with invasive bladder cancer. The aim of the study was to examine Total PSA, Free PSA, and Free/Total Ratio elimination kinetics after radical cystoprostatectomy.

METHODS

Serum PSA, Free PSA, and Free/Total Ratio were determined preoperatively, at the time of cystoprostatectomy specimen removal and then at 3, 6, 12, 24, 48, 72, and 168 hr, from seven patients with muscle invasive bladder cancer, who underwent radical cystoprostatectomy. Free and Total PSA concentrations were measured with non-competitive immunological procedures. The elimination rates and half-lives of Total, Free PSA and Free/Total Ratio were studied using a nonlinear regression analysis.

RESULTS

Surgical manipulations caused about 1.5-fold increase of PSA, 5-fold increase in Free PSA and 3-fold increase in Free/Total Ratio. PSA and Free PSA followed a biphasic elimination pattern of a rapid exponential (a) phase with a half-life of 4.27 and 2.14 hr and a terminal, nonexponential (b) phase with a half-life of 63 and 173.2 hr, respectively. Free/Total PSA Ratio followed, also, a biphasic kinetic pattern of a rapid exponential decline with a half-life of 3.34 and a terminal non-exponential increase with a doubling time of 43 hr.

CONCLUSIONS

Comparing PSA kinetics after radical cystoprostatectomy with those of radical prostatectomy, it appears that PSA follows the same elimination pattern in both models. In contrast, Free PSA and Free/Total Ratio elimination kinetics' patterns differ between the two surgical models.

Advantages of prostate-specific antigen (PSA) clearance model over simple PSA half-life computation to describe PSA decrease after prostate adenomectomy

OBJECTIVES

A population kinetic approach based on PSA clearance (CL(PSA)) may be a more rational strategy to characterize prostate-specific antigen (PSA) decrease profile after prostate surgery than the commonly used method (half-life from mono/bi-exponential models).

METHODS

We used 182 post-adenomectomy PSA concentrations from 56 benign prostatic hyperplasia patients to build, with NONMEM software, a multi-exponential and a CL(PSA) model for comparison.

RESULTS

The best multi-exponential model was PSA(t)=4.96e(-)(0.269t)+3.10e(-)(0.16t)+0.746e(+)(0.0002t) with a stable median residual PSA at 0.64 ng/mL. The best model parametrized with clearance was CL(PSA)=0.0229()(AGE/69)(3.78). Akaike information criteria and standard errors favored the CL(PSA) model. Median peripheral zone and transitional zone productions were 0.034 ng/mL/cm(3) and 0.136 ng/mL/g. A threshold at 2 ng/mL on day 90 allowed for a diagnostic of biochemical relapse diagnostic.

CONCLUSIONS

The population CL(PSA) model was superior to the multi-exponential approach for investigating individual post-adenomectomy PSA decreases.

PSA elevation during prostate cryosurgery and subsequent decline

PURPOSE

To determine the immediate effect of prostate cryosurgery on PSA and the subsequent decline.

METHODS AND MATERIALS

PSA level was measured in 14 patients who underwent cryosurgery for prostate cancer. Blood samples were taken immediately before and after cryosurgery and 1, 2, 4, 6 weeks and 3 months postoperatively. A confidence interval for the elevation from baseline to maximal PSA was calculated. PSA decline was assessed in patients with a nadir PSA < or =0.5 ng/mL. Patients with a postoperative nadir PSA >0.5 ng/mL were considered to harbor viable cancer and were excluded from the decline analysis. The observed PSA levels during the postoperative period were compared with the expected levels that were calculated according to the maximal PSA level and a serum half-life of 2.5 days. Student t-test was used to compare expected and observed PSA levels.

RESULTS

PSA increased from an average of 9.23 ng/mL preoperatively to a maximum average of 155 ng/mL (maximal PSA ranges: 18.9-490.5 ng/mL). The 95% CI for the increase in PSA from baseline level was 63.4 to 224.14. PSA nadir < or =0.5 ng/mL was achieved in 10 patients. The observed PSA decline course was slower than expected according to its half-life. Average observed and expected PSA levels at 2,4 and 6 weeks after cryosurgery were 10.4 versus 3.57 ng/mL (P = 0.005), 0.65 versus 0.07 (P = 0.007) and 0.09 versus 0.001 (P = 0.03), respectively.

CONCLUSION

PSA levels increase steeply following cryosurgery, and decline slower than expected according to the serum half-life.

[Prostate cancer recurrence after radical prostatectomy and salvage radiotherapy]

OBJECTIVE

To evaluate the efficacy of the radiotherapy to prostatic bed in patients with biochemical recurrence for prostate cancer after radical prostatectomy.

MATERIAL AND METHODS

We analyse the results of 292 patients underwent radical prostatectomy for localized prostate cancer T1-T2 between January 1992 and June 2003, with an average folow-up of 36 months (range 6 months to 12 years). We detect biochemical recurrence (PSA >0.20 ng/ml) in 75 (26%) patients. Of 75 patients with biochemical recurrence, 9 (12%) was diagnosed of local recurrence by the following criteria: a) The first PSA obtained 6 weeks after radical prostatectomy <0.20 ng/ml. b) The time to biochemical recurrence >6 months. c) The prostate specific antigen doubling time >6 months. d) The prostate specific antigen velocity after radical prostatectomy <0.75 ng/ml/year. e) The prostate specific antigen level after radical prostatectomy <2.5 ng/ml. The 9 patients diagnosed of local recurrence received an average dose of 56.42 Gy in the prostate bed.

RESULTS

Of all 9 patients with local recurrence, 7 (77.7%) has complete response with an average time of follow-up of 25 months (6-30 months). The time between the radiotherapy and the response, in patients with complete response, was lower than 3 months. Were not observed significant adverse effects associated to radiotherapy.

CONCLUSIONS

The salvage radiotherapy may be beneficial in select patients with local recurrence. The characteristics of prostate specific antigen elevation are useful in distinguishing men with local recurrence from those with distant metastases.

cPSA and fPSA elimination in African-American men

In all, 22 African-American males undergoing radical prostatectomy for prostate adenocarcinoma had serum drawn for tPSA, cPSA, and total protein concentrations prior to, during, and after operation to determine the respective elimination rates. African-American cPSA was found to fit best a simple first-order exponential elimination kinetic, with a half-life of 44.6 h. fPSA followed a two-compartment elimination with an alpha-phase elimination of 0.50 h and a beta-phase half-life of 4.2 h. Our results suggest higher rates of elimination for both cPSA and fPSA in an African-American male population with respect to Caucasians and may account for differences in PSA values between races.

Prostate cancer: radical prostatectomy

Today, more men than ever before are being followed after radical prostatectomy. Prognosis and follow-up should be based on the pathologic specimen. Measurable prostate-specific antigen (PSA) after surgery defines failure, with time to detectable PSA and rate of PSA rise being useful prognostic factors. The natural history of untreated biochemical failure is protracted, a fact to be considered in discussions of adjuvant treatment. Early in disease recurrence, imaging studies to locate residual disease rarely are useful clinically. Both adjuvant and salvage radiation to the prostate bed have benefits and risks, but neither is superior in overall prostate cancer survival. The timing of hormone therapy remains largely empiric. The promise of effective cytotoxic chemotherapy still is greater than its actual benefits, although novel cytostatic agents are being developed. The future management of this disease will improve with better molecular definition of risk and therapeutic response.

Kinetics of Serum Tumor Marker Concentrations and Usefulness in Clinical Monitoring

Only a few markers have been instrumental in the diagnosis of cancer. In contrast, tumor markers play a critical role in the monitoring of patients. The patient’s clinical status and response to treatment can be evaluated rapidly using the tumor marker half-life (t1/2) and the tumor marker doubling time (DT). This report reviews the interest of determining these kinetic parameters for prostate-specific antigen, human chorionic gonadotropin, α-fetoprotein, carcinoembryonic antigen, cancer antigen (CA) 125, and CA 15-3. A rise in tumor markers (DT) is a yardstick with which benign diseases can be distinguished from metastatic disease, and the DT can be used to assess the efficacy of treatments. A decline in the tumor marker concentration (t1/2) is a predictor of possible residual disease if the timing of blood sampling is soon after therapy. The discrepancies in results obtained by different groups may be attributable to the multiplicity of immunoassays, the intrinsic characteristics of each marker (e.g., antigen specificity, molecular heterogeneity, and associated forms), individual factors (e.g., nonspecific increases and renal and hepatic diseases) and methods used to calculate kinetics (e.g., exponential models and timing of blood sampling). This kinetic approach could be of interest to optimize patient management.

Serum half-life time determination of free and total prostate-specific antigen following radical prostatectomy--a critical assessment

OBJECTIVES

All studies investigating the elimination kinetics of serum total (tPSA) and free (fPSA) prostate-specific antigen (PSA) were carried out in men undergoing radical prostatectomy. Radical prostatectomy itself could, however, have a major influence on the serum concentration of these tumor markers (e.g., perioperative fluid shift or blood loss). The purpose of our study was to determine the half-life time of fPSA and tPSA with special regard to the influence of the radical prostatectomy on the serum concentration of these tumor markers.

METHODS

Eleven men (mean age 63.2+/-7.2 years) with organ-confined prostate cancer who underwent radical prostatectomy were investigated (final pathologic Stage pT2pN0 or lower). Serum samples were obtained preoperatively and 0.25, 0.5, 1, 2, 4, 8, 12, 16, 24, 48, 72, 120, 168, and 240 hours after removal of the prostate. fPSA and tPSA and albumin and total protein serum concentrations were determined in all samples.

RESULTS

During the first 120 minutes after removal of the prostate, albumin and total protein serum concentrations continuously declined, with a half-life time of -104.5+/-28 minutes and -129.7+/-32 minutes, respectively. Serum decline of fPSA and tPSA followed a biphasic kinetic. During the initial alpha-phase, fPSA and tPSA serum concentrations decreased, with a half-life time of -69+/-10.3 minutes and -87.3+/-18.1 minutes, respectively. During the terminal beta-phase, the half-life time of fPSA and tPSA was -1152.2 minutes (0.8 days) and -3916.1 minutes (2.7 days), respectively. Between the alpha-phase half-life time of fPSA or tPSA and the half-life time of the total protein or albumin concentration decline, significant correlations were found.

CONCLUSIONS

These correlations indicate that the rapid decline of fPSA and tPSA directly after removal of the prostate (alpha-phase half-life time) is caused by the radical prostatectomy itself. The half-life time of the beta-phase reflects the biologic clearance of PSA. Therefore, the half-life time determination of PSA after radical prostatectomy is of limited value if the influence of the operation itself on the serum PSA concentration is not taken into account.

Rapid exponential elimination of free prostate-specific antigen contrasts the slow, capacity-limited elimination of PSA complexed to alpha 1-antichymotrypsin from serum

OBJECTIVES

To study the rates of elimination of total prostate-specific antigen (PSA-T), free PSA (PSA-F), and PSA complexed to alpha 1-antichymotrypsin (PSA-ACT) from blood after radical retropubic prostatectomy (RRP).

METHODS

We obtained venous blood from 10 patients with prostate cancer who were undergoing RRP. We analyzed PSA-F and PSA-ACT and equimolar detection of both of these forms together (PSA-T) by using immunofluorometric assays. An attempt was made to fit the serum concentrations of PSA-F, PSA-ACT, and PSA-T for each patient to exponential curves by applying one- and two-compartment models for pharmacokinetic analysis.

RESULTS

Manipulation of the prostate during RRP resulted in a 3- to 28-fold increase in PSA-F concentrations in serum. Removal of the prostate resulted in a rapid, biexponential elimination of PSA-F from serum, corresponding to a mean initial (alpha) half-life of 0.81 hours and a mean terminal (beta) half-life of 13.9 hours. Serum PSA-ACT concentrations decreased by 20% to 40% immediately after removal of the gland; the elimination after surgery was slow and nonexponential, corresponding to a mean rate of 0.8 ng/mL/day. The elimination of PSA-T reflects a combination of the elimination patterns for PSA-F and PSA-ACT.

CONCLUSIONS

The main proportion of PSA-F is rapidly eliminated from serum, possibly by glomerular filtration. PSA-F released during surgery did not form complexes with ACT, as suggested by the lack of PSA-ACT elevation in serum. The size (approximately 90 kDa) and the extensive in vitro stability of the PSA-ACT complex prevents renal clearance. The nonexponential elimination of the PSA-ACT complex is evidence of a capacity-limited process (e.g., metabolic transformation).

Elimination of serum free and total prostate-specific antigen after radical retropubic prostatectomy

Elimination kinetics of serum total and free prostate-specific antigen were studied for a ten days course after radical retropubic prostatectomy on 11 patients suffering from organ confined prostate cancer. Samples were taken before operation, immediately after finishing the operation and 1, 2, 3, 4, 5, 6 h after prostatectomy and then once a day for the following ten days. The measurements were performed with AxSym assays from Abbott Laboratories. The elimination of both total and free prostate-specific antigen followed a biphasic kinetics. In the fast phase, the average of the individual elimination half-lives of total and free prostate-specific antigen amounted to 6.3 h (SD = 6.1 h; range: 0.55 to 37.1 h) and 0.57 h (SD = 0.18 h; range: 0.22 to 0.89 h), respectively. In the slow phase, total prostate-specific antigen disappeared with an average half-life of 85.6 h (SD = 11 h; range: 47.2 to 261.7 h) and free prostate-specific antigen with an average half-life of 14.4 h (SD = 10.4 h; range: 2.4 to 30.3 h). These results might be significant for the use of free and total prostate-specific antigen and its ratio as a diagnostic and prognostic tool.