Quantification of prostatic cancer metastatic disease using prostate-specific antigen

The analysis of some factors that influence on serum PSA level in localized prostate cancer patients: mathematical model

INTRODUCTION

Serum prostate specific antigen (PSA) concentration in localized prostate cancer (PCa) patients depends of numerous factors related to tumor, prostate and the patient. Tumor factors include tumor volume, localization, growth rate and aggressiveness. Prostate factors include prostate volume, the activity of dihydrotestosterone (DHT) and PSA synthesis. Host factors include androgenic status and total blood volume.

OBJECTIVE

to discuss all the possible factors that influence on serum PSA levels in localized PCa patients. To present the mathematical model that predicts serum PSA concentration in localized PCa patients.

METHODS

Mathematical model is based on the hypothesis that tumor-related PSA molecules are released from the epithelial prostatic cells around the tumor, so called "Destruction Zone" around the tumor (DZ). The amount of PSA is dependent of DZ volume. Moreover, DZ volume depends on tumor volume, tumor localization in the prostate and tumor growth rate.

RESULTS

The study offers the wide spectrum of PSA values, dependent on tumor, prostate and patient characteristics. These values are comparable with the empirical results in the literature, especially if tumor-volume doubling time of three years is entered into the calculations.

CONCLUSION

Although with some limitations, this mathematical model can explain the great variety of PSA serum concentrations in PCa patients.

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.

Urinary prostate specific antigen: is the clinical use likely?

Prostate specific antigen (PSA) blood test represents the standard procedure in prostate cancer (CaP) diagnosis and follow-up. However, determination of PSA in the urine, where PSA is present in much higher concentrations than in the blood, still remains in the field of research.

OBJECTIVES

To determine urinary concentrations of PSA (uPSA) in different groups of patients (pts.), and to estimate is it possible to differentiate benign and malignant prostate diseases and to follow-up the results of treatment.

METHODS

Between January 2001. and November 2003., urinary concentrations of PSA were determined at 142 pts. divided in seven groups: 1. young and healthy volunteers, 2. "BPH-24": pts. with benign prostatic hyperplasia (BPH) who collected the sample of 24-hour voided urine, 3. "BPH-I": pts. with BPH who collected the first portion of first urinary voiding, 4. "TRUS-CaP": pts. with CaP which gave the first portion of urine just prior to transrectal ultrasound-guided prostate biopsy (TRUS- biopsy), 5. "TRUS-non-CaP": pts. who gave first portion of urine prior to TRUS-biopsy, but biopsy did not prove the presence of CaP, 6. "RRP": pts. who underwent radical retropubic prostatectomy (RRP), 7. "AAT": pts. who underwent androgen deprivation therapy.

RESULTS

Average uPSA value in the group of young and healthy volunteers, was 13.8 +/- 19.6 ng/ml, in "BPH-24": 38.0 +/- 44.4 ng/ml, in "BPH-I": 140.8 +/- 140.9 ng/ml, in "TRUS-CaP": 234.8 +/- 277.7 ng/ml, in TRUS-non-CaP: 113.1 +/- 148.5 ng/ml, and in the group "RRP": 4.4 +/- 4.7 ng/ml. There was no statistically significant difference of average uPSA values between "BPH-I" and "TRUS-CaP" groups. The significant difference was found between the group of young volunteers and "BPH-I". In "TRUS-CaP" group, there was strong correlation between tumour size and aggressivenes and uPSA concentration. Finally, PSA and uPSA decline during androgen deprivation therapy, strongly correlated (up to r = 0.95).

CONCLUSIONS

Determination of uPSA cannot differentiate BPH and CaP. However, in the group of pts. with proven localized CaP, uPSA can provide additional information concerning T-staging. Moreover, simultaneous monitoring of PSA and uPSA response on hormonal therapy, can provide an early recognition of androgen-indiferent CaP (AIPCA) and hormone-resistent CaP (HRPCA).

Influence of benign prostatic hyperplasia, testosterone and age on serum levels of prostate specific antigen

Prostate specific antigen (PSA) and PSA-density (PSAd) were studied in 120 symptomatic patients with benign prostatic hyperplasia at digital rectal examination. PSA and PSAd were measured before and 3 months after transurethral resection. Comparisons were made between patients in whom histologic examination showed benign hyperplasia and those with histologically demonstrated prostatic cancer. The influence of age and of serum testosterone on PSA and PSAd was determined. PSAd in benign prostatic hyperplasia was the same in the transition zone (the adenomas) and the peripheral zone (mean 0.065), indicating no increased synthesis or leakage of PSA. PSAd with cut-off value 0.10 ng x ml-1 x cc-1 showed higher sensitivity and positive predictive value (75% vs 50% and 0.33 vs 0.15, respectively) in nonpalpable prostatic cancer than did PSA with cut-off at 4 ng x ml-1. No statistically significant influence of testosterone and/or age on serum-PSA or PSAd was found.

Serum concentration of prostate-specific antigen in relation to prostate volume in 50 healthy middle-aged men

Fifty men without symptoms of prostatic disease, aged 40 to 66 years, were studied with respect to serum concentration of prostate-specific antigen (PSA) and volume of the prostate gland. PSA was determined with two immunometric assays, one using a radioactive label, the other a nonisotopic label. Prostate volume was determined by transrectal ultrasound examination using two different modes of evaluation and assessed by rectal examination. The simpler "ellipsoid method" underestimated the volume by 20% compared to planimetry of several sections but they were well correlated to each other. It was found that prostate volume increased by 0.4 ml per year of age increase. There was a curvilinear relationship between serum PSA concentration and prostate volume determined by ultrasound; no statistically significant relationship was found between PSA concentration and prostate volume by rectal examination. The results indicate that the diagnostic value of serum PSA, for prostatic malignancy, will increase if values are related to prostate volume determined by ultrasound examination.