Similar rates of exponential decrease in serum concentrations of free prostate-specific antigen (PSA), PSA complexed to alpha-1-antichymotrypsin, and human glandular kallikrein 2 (hK2) in prostate cancer patients treated with GnRH-analogues

Androgen deprivation decreases prostate specific antigen in the absence of tumor: implications for interpretation of PSA results

Background: Prostate-specific antigen (PSA) is used as an outcome measure for relapsed disease in prostate cancer. Nonetheless, there are considerable concerns about its indiscriminate use as a surrogate endpoint for cell growth or survival. We hypothesized that treatment with a luteinizing hormone releasing hormone (LHRH) analog would decrease PSA levels even in the absence of malignant disease.

Methods: We determined testosterone and PSA levels in 30 healthy volunteers after a single intramuscular injection of a LHRH depot formulation. Testosterone and PSA levels were quantified by radioimmunoassay and electrochemi-luminescence immunoassay, respectively.

Results: After an initial flare-up during the first 3 days testosterone decreased reaching castration levels in 18 of the 30 young men (60%). After the nadir on day 28, testosterone levels increased to normal again. Changes in PSA paralleled those of testosterone. Castration reduced PSA levels by 29% (95% CI 19%–39%) compared to baseline (p<0.0001).

Conclusions: LHRH superagonists decrease PSA levels by testosterone deprivation. Conferring these findings to tumor patients, decreases in PSA after treatment with LHRH analogs might not only reflect disease regression but also a direct testosterone mediated effect on PSA. Thus, PSA levels should be cautiously interpreted when patients receive hormonal therapy.

Rapid elimination kinetics of free PSA or human kallikrein-related peptidase 2 after initiation of gonadotropin-releasing hormone-antagonist treatment of prostate cancer: potential for rapid monitoring of treatment responses

BACKGROUND

The utility of conventional prostate-specific antigen (PSA) measurements in blood for monitoring rapid responses to treatment for prostate cancer is limited because of its slow elimination rate. Prior studies have shown that free PSA (fPSA), intact PSA (iPSA) and human kallikrein-related peptidase 2 (hK2) are eliminated more rapidly after radical prostatectomy. In contrast, all three markers have similarly slow elimination rates after castration induced by gonadotropin-releasing hormone (GnRH) agonists, possibly due to the slow onset of castration. Therefore, we assessed elimination rates of tPSA, fPSA, iPSA and hK2 after rapid induction of castration with degarelix (Firmagon(®)), a novel GnRH antagonist.

METHODS

This study included 24 patients treated with degarelix. Blood was taken at 1, 3, 7, 14, 21 and 28 days after injection of degarelix. Free and total PSA were measured with a commercial dual-label assay, and with inhouse research assays of intact PSA and hK2.

RESULTS

Median (interquartile range, IQR) tPSA at baseline was 23.4 (15.8, 59.8). Twenty-two patients (92 % ) reached castrate levels of testosterone within 24 h of degarelix initiation, and all patients did so within 72 h. All kallikrein forms declined in an exponential fashion after degarelix administration. The median time to 50 % reduction in biomarker level was 8 – 9 days for tPSA or complexed PSA vs. 2-4 days for hK2, iPSA and fPSA. The percentage eliminated at day 3 and day 7 was significantly higher for hK2, iPSA and fPSA than for tPSA (all p < 0.02), while tPSA and complexed PSA were similar.

CONCLUSIONS

The rapid decline of fPSA, iPSA and hK2 after fast induction of castration with degarelix is similar to that reported after prostatectomy and offers a novel, informative method to monitor rapid onset of therapeutic action targeting signaling of the androgen receptor.

Serum PSA half-life as a predictor of survival for hormone-refractory prostate cancer patients: modelization using a standardized set of response criteria

OBJECTIVE

Changes of serum prostate-specific antigen (PSA) during chemotherapy have been validated as a marker of response for hormone-refractory prostate cancer (HRPC) patients. We retrospectively established new response criteria to assess the risk of death.

METHODS

Two hundred fifty-six chemonaive HRPC patients treated with chemotherapy were included in the analysis. According to PSA half-life (HL) dynamics, three response categories were defined: responders (R), late-progressors (LP) and initial-progressors (IP), that were compared with Working Group (WG) criteria. PSA HL time to failure (TTF) and overall survival (OS) were estimated and compared between HT categories. Multivariate regression analysis was performed to isolate the impact on OS of these response categories. A new predictor of survival, delta-time PSA interval (DeltaT) was described.

RESULTS

PSA HL categories were strongly related with WG criteria (P = 0.0001). PSA HL TTF differed among PSA HL categories: 4.2, 2.3, and 0.9 months for R, LP, and IP patients, respectively, and their respective median OS were 27, 19.7, and 12.3 months (P = 0.0001). For DeltaT > or = 3 versus <3 months, median OS significantly differed: 24.9 months versus 13.2 months (P = 0.0001).

CONCLUSIONS

PSA HL dynamics during chemotherapy were able to accurately predict survival, earlier than WG-defined progression criteria. This criterion should be prospectively evaluated in randomized trials for HRPC patients in order to better estimate the risk of death.