Prostate-specific Antigen Bounce After Stereotactic Body Radiotherapy for Prostate Cancer: A Pooled Analysis of Four Prospective Trials

Refining the definition of biochemical failure in the era of stereotactic body radiation therapy for prostate cancer: The Phoenix definition and beyond

BACKGROUND AND PURPOSE

The Phoenix definition for biochemical failure (BCF) after radiotherapy uses nadir PSA (nPSA) + 2 ng/mL to classify a BCF and was derived from conventionally fractionated radiotherapy, which produces significantly higher nPSAs than stereotactic body radiotherapy (SBRT). We investigated whether an alternative nPSA-based threshold could be used to define post-SBRT BCFs.

MATERIALS AND METHODS

PSA kinetics data on 2038 patients from 9 institutions were retrospectively analyzed for low- and intermediate-risk PCa patients treated with SBRT without ADT. We evaluated the performance of various nPSA-based definitions. We also investigated the relationship of relative PSA decline (rPSA, PSA_18month/PSA_6month) and timing of reaching nPSA + 2 with BCF.

RESULTS

Median follow-up was 71.9 months. BCF occurred in 6.9% of patients. Median nPSA was 0.16 ng/mL. False positivity of nPSA + 2 was 30.2%, compared to 40.9%, 57.8%, and 71.0% for nPSA + 1.5, nPSA + 1.0, and nPSA + 0.5, respectively. Among patients with BCF, the median lead time gained from an earlier nPSA + threshold definition over the Phoenix definition was minimal. Patients with BCF had significantly lower rates of early PSA decline (mean rPSA 1.19 vs. 0.39, p < 0.0001) and were significantly more likely to reach nPSA + 2 ≥ 18 months (83.3% vs. 21.1%, p < 0.0001). The proposed criterion (rPSA ≥ 2.6 or nPSA + 2 ≥ 18 months) had a sensitivity and specificity of 92.4% and 81.5%, respectively, for predicting BCF in patients meeting the Phoenix definition and decreased its false positivity to 6.4%.

CONCLUSION

The Phoenix definition remains an excellent definition for BCF post-SBRT. Its high false positivity can be mitigated by applying additional criteria (rPSA ≥ 2.6 or time to nPSA + 2 ≥ 18 months).

Prognostic value of PSA bounce in prostate cancer following definitive radiation therapy: a systematic review and meta-analysis

BACKGROUND

The prognostic significance of PSA bounce following definitive radiation therapy remains controversial. To develop a sense of current opinion in this area, we performed a systematic search of the literature based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

METHODS

In January 2021, we systematically searched PubMed, the Cochrane library, and Scopus for studies that compared patients who had localized prostate cancer with or without PSA bounce after definitive radiation therapy. Our objective was to evaluate the association of PSA bounce with biochemical recurrence-free survival, metastatic-free survival, cancer-specific survival, and overall survival, using multivariate Cox regression analysis.

RESULTS

A total of 8881 patients in 10 studies matched the selection criteria for the systematic review and meta-analysis. The number of patients with PSA bounce accounted for 2706 of all 8881 patients (30.5%). PSA bounce was associated with better biochemical recurrence-free survival after definitive radiation therapy (pooled HR: 0.62, 95% CI: 0.54-0.71). Subgroup analyses also showed that PSA bounce was independently associated with decreased risk for biochemical recurrence-free survival in prostate cancer patients treated with low dose rate brachytherapy alone (pooled HR: 0.38, 95% CI: 0.27-0.55) and external beam radiotherapy alone (pooled HR: 0.71, 95% CI: 0.57-0.87).

CONCLUSIONS

This meta-analysis indicated that PSA bounce after definitive radiation therapy is related to improved outcome in terms of biochemical failure in prostate cancer patients.

Prostate-specific antigen (PSA) bounce following salvage radiotherapy to the prostate bed in a patient with prostate cancer post-prostatectomy

We present a case of prostate-specific antigen (PSA) bounce in a 76 year old man who underwent salvage radiotherapy to the prostate bed following biochemical relapse 6 years post-radical prostatectomy for a T2N0 Gleason grade 3 + 3 prostate adenocarcinoma; 10 months following completion of salvage radiotherapy for biochemical PSA recurrence of 0.2 μg/L. Following undetectable results (<0.03 μg/L), his PSA rose from 0.04 to 0.3 μg/L with no evidence of prostate cancer recurrence before returning to undetectable levels without medical intervention. This PSA 'bounce phenomenon' is well described following radiotherapy to an intact prostate and has been proposed to be the result of a late fibrotic effect on irradiated prostate tissue. To our knowledge, this is the first case published describing the effect in the post-prostatectomy setting. It highlights the importance of serial PSA monitoring to confirm biochemical relapse before committing the patient to androgen deprivation therapy (with its inherent risks and side effects).

Characteristics of PSA Bounce after Radiotherapy for Prostate Cancer: A Meta-Analysis

The rate and characteristics of prostate-specific antigen (PSA) bounce post-radiotherapy remain unclear. To address this issue, we performed a meta-analysis. Reports of PSA bounce post-radiotherapy with a cutoff of 0.2 ng/mL were searched by using Medline and Web of Science. The primary endpoint was the occurrence rate, and the secondary endpoints were bounce characteristics such as amplitude, time to occurrence, nadir value, and time to nadir. Radiotherapy modality, age, risk classification, androgen deprivation therapy, and the follow-up period were extracted as clinical variables. Meta-analysis and univariate meta-regression were performed with random-effect modeling. Among 290 search-positive studies, 50 reports including 26,258 patients were identified. The rate of bounce was 31%; amplitude was 1.3 ng/mL; time to occurrence was 18 months; nadir value was 0.5 ng/mL; time to nadir was 33 months. Univariate meta-regression analysis showed that radiotherapy modality (29.7%), age (20.2%), and risk classification (12.2%) were the major causes of heterogeneity in the rate of bounce. This is the first meta-analysis of PSA bounce post-radiotherapy. The results are useful for post-radiotherapy surveillance of prostate cancer patients.