Integrating Prostate-specific Antigen Kinetics into Contemporary Predictive Nomograms of Salvage Radiotherapy After Radical Prostatectomy

Development and Internal Validation of a Novel Nomogram Predicting the Outcome of Salvage Radiation Therapy for Biochemical Recurrence after Radical Prostatectomy in Patients without Metastases on Restaging Prostate-specific Membrane Antigen Positron Emission Tomography/Computed Tomography

Background and objective

Owing to the greater use of prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) in patients with biochemical recurrence (BCR) of prostate cancer (PCa) after robot-assisted radical prostatectomy (RARP), patient selection for local salvage radiation therapy (sRT) has changed. Our objective was to determine the short-term efficacy of sRT in patients with BCR after RARP, and to develop a novel nomogram predicting BCR-free survival after sRT in a nationwide contemporary cohort of patients who underwent PSMA PET/CT before sRT for BCR of PCa, without evidence of metastatic disease.

Methods

All 302 eligible patients undergoing PCa sRT in four reference centers between September 2015 and August 2020 were included. We conducted multivariable logistic regression analysis using a backward elimination procedure to develop a nomogram for predicting biochemical progression of PCa, defined as prostate-specific antigen (PSA) ≥0.2 ng/ml above the post-sRT nadir within 1 yr after sRT.

Key findings and limitations

Biochemical progression of disease within 1 yr after sRT was observed for 56/302 (19%) of the study patients. The final predictive model included PSA at sRT initiation, pathological grade group, surgical margin status, PSA doubling time, presence of local recurrence on PSMA PET/CT, and the presence of biochemical persistence (first PSA result ≥0.1 ng/ml) after RARP. The area under the receiver operating characteristic curve for this model was 0.72 (95% confidence interval 0.64-0.79). Using our nomogram, patients with a predicted risk of >20% had a 30.8% chance of developing biochemical progression within 1 yr after sRT.

Conclusions

Our novel nomogram may facilitate better patient counseling regarding early oncological outcome after sRT. Patients with high risk of biochemical progression may be candidates for more extensive treatment.

Patient summary

We developed a new tool for predicting cancer control outcomes of radiotherapy for patients with recurrence of prostate cancer after surgical removal of their prostate. This tool may help in better counseling of these patients with recurrent cancer regarding their early expected outcome after radiotherapy.

How the Management of Biochemical Recurrence in Prostate Cancer Will Be Modified by the Concept of Anticipation and Incrementation of Therapy

Biochemical recurrence (BCR) after primary treatments for prostate cancer (PC) is an extremely heterogeneous phase and at least a stratification into low- and high-risk cases for early progression in metastatic disease is necessary. At present, PSA-DT represents the best parameter to define low- and high-risk BCR PC, but real precision medicine is strongly suggested to define tailored management for patients with BCR. Before defining management, it is necessary to exclude the presence of low-volume metastasis associated with PSA progression using new-generation imaging, preferably with PSMA PET/CT. Low-risk BCR cases should be actively observed without early systemic therapies. Early treatment of low-risk BCR with continuous androgen deprivation therapy (ADT) can produce disadvantages such as the development of castration resistance before the appearance of metastases (non-metastatic castration-resistant PC). Patients with high-risk BCR benefit from early systemic therapy. Even with overall survival (OS) as the primary treatment endpoint, metastasis-free survival (MFS) should be used as a surrogate endpoint in clinical trials, especially in long survival stages of the disease. The EMBARK study has greatly influenced the management of high-risk BCR, by introducing the concept of anticipation and intensification through the use of androgen receptor signaling inhibitors (ARSIs) and ADT combination therapy. In high-risk (PSA-DT ≤ 9 months) BCR cases, the combination of enzalutamide with leuprolide significantly improves MFS when compared to leuprolide alone, maintaining an unchanged quality of life in the asymptomatic phase of the disease. The possibility of using ARSIs alone in this early disease setting is suggested by the EMBARK study (arm with enzalutamide alone) with less evidence than with the intensification of the combination therapy. Continued use versus discontinuation of enzalutamide plus leuprolide intensified therapy upon reaching undetectable PSA levels needs to be better defined with further analysis. Real-world analysis must verify the significant results obtained in the context of a phase 3 study.

Multi-institutional Development and External Validation of a Machine Learning Model for the Prediction of Distant Metastasis in Patients Treated by Salvage Radiotherapy for Biochemical Failure After Radical Prostatectomy

BACKGROUND

Up to 40% of patients with prostate cancer may develop biochemical recurrence after surgery, with salvage radiation therapy (SRT) being the only curative option. In 2016, Tendulkar et al. (Contemporary update of a multi-institutional predictive nomogram for salvage radiotherapy after radical prostatectomy. J Clin Oncol 2016;34:3648-54) published a nomogram to predict distant metastasis in a cohort of patients treated with SRT with pre-SRT prostate-specific antigen (PSA) of 0.5 ng/ml after radical prostatectomy. In modern practice, SRT is delivered at lower PSA values.

OBJECTIVE

To train and externally validate a machine learning model to predict the risk of distant metastasis at 5 yr in a contemporary cohort of patients receiving SRT.

DESIGN, SETTING, AND PARTICIPANTS

We trained a machine learning model on data from 2418 patients treated with SRT at one institution, with a median PSA value of 0.27 ng/ml. External validation was done in 475 patients treated at two different institutions. Patients with cM1, pN1, or pT4 disease were excluded, as were patients with PSA >2 ng/ml or PSA 0, and patients with radiation dose <60 or ≥80 Gy.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Model performance was assessed using calibration and time-dependent area under the receiver operating curve (tAUC).

RESULTS AND LIMITATIONS

Our model had better calibration and showed improved discrimination (tAUC = 0.72) compared with the Tendulkar model (tAUC = 0.60, p < 0.001). The main limitations of this study are its retrospective design and lack of validation on patients who received hormone therapy.

CONCLUSIONS

The updated model can be used to provide more individualized risk assessments to patients treated with SRT at low PSA values, improving decision-making.

PATIENT SUMMARY

Up to 40% of patients with prostate cancer may develop biochemical recurrence after surgery, with salvage radiation therapy as the only potentially curative option. We trained and validated a machine learning model using clinical and surgical data to predict a patient's risk of distant metastasis at 5 yr after treatment. Our model outperformed the reference tool and can improve clinical decision-making by providing more personalized risk assessment.

Can PSMA PET/CT help in dose-tailoring in post-prostatectomy radiotherapy?

There are few randomized trials to evaluate the use of PSMA-PET in the planning of post-prostatectomy radiotherapy. There are two unresolved questions 1) should we increase the dose to lesions visible on PSMA-PET 2) can we reduce dose in the case of a negative PSMA-PET. In this review, we summarize and discuss the available evidence in the literature. We found that in general, there seems to be an advantage for dose-increase, but ta large recent study from the pre-PSMA era didn't show an advantage for dose escalation. Retrospective studies have shown that conventional doses to PSMA-PET-positive lesions seem sufficient. On the other hand, in the case of a negative PSMA-PET, there is no evidence that dose-reduction is possible. In the future, the combination of PSMA-PET with genomic classifiers could help in better identify patients who might benefit from either dose- de-or -increase. We further need to identify intraindividual references to help identify lesions with higher aggressiveness.

Biochemical Recurrence and Risk of Mortality Following Radiotherapy or Radical Prostatectomy

Importance

Stratifying patients with biochemical recurrence (BCR) after primary treatment for prostate cancer based on the risk of prostate cancer-specific mortality (PCSM) is essential for determining the need for further testing and treatments.

Objective

To evaluate the association of BCR after radical prostatectomy or radiotherapy and its current risk stratification with PCSM.

Design, Setting, and Participants

This population-based cohort study included a total of 16 311 male patients with 10 364 (64%) undergoing radical prostatectomy and 5947 (36%) undergoing radiotherapy with curative intent (cT1-3, cM0) and PSA follow-up in Stockholm, Sweden, between 2003 and 2019. Follow-up for all patients was until death, emigration, or end of the study (ie, December 31, 2018). Data were analyzed between September 2022 and March 2023.

Main Outcomes and Measures

Primary outcomes of the study were the cumulative incidence of BCR and PCSM. Patients with BCR were stratified in low- and high-risk according to European Association of Urology (EAU) criteria.

Exposures

Radical prostatectomy or radiotherapy.

Results

A total of 16 311 patients were included. Median (IQR) age was 64 (59-68) years in the radical prostatectomy cohort (10 364 patients) and 69 (64-73) years in the radiotherapy cohort (5947 patients). Median (IQR) follow-up for survivors was 88 (55-138) months and 89 (53-134) months, respectively. Following radical prostatectomy, the 15-year cumulative incidences of BCR were 16% (95% CI, 15%-18%) for the 4024 patients in the low D'Amico risk group, 30% (95% CI, 27%-32%) for the 5239 patients in the intermediate D'Amico risk group, and 46% (95% CI, 42%-51%) for 1101 patients in the high D'Amico risk group. Following radiotherapy, the 15-year cumulative incidences of BCR were 18% (95% CI, 15%-21%) for the 1230 patients in the low-risk group, 24% (95% CI, 21%-26%) for the 2355 patients in the intermediate-risk group, and 36% (95% CI, 33%-39%) for the 2362 patients in the high-risk group. The 10-year cumulative incidences of PCSM after radical prostatectomy were 4% (95% CI, 2%-6%) for the 1101 patients who developed low-risk EAU-BCR and 9% (95% CI, 5%-13%) for 649 patients who developed high-risk EAU-BCR. After radiotherapy, the 10-year PCSM cumulative incidences were 24% (95% CI, 19%-29%) for the 591 patients in the low-risk EAU-BCR category and 46% (95% CI, 40%-51%) for the 600 patients in the high-risk EAU-BCR category.

Conclusions and Relevance

These findings suggest the validity of EAU-BCR stratification system. However, while the risk of dying from prostate cancer in low-risk EAU-BCR after radical prostatectomy was very low, patients who developed low-risk EAU-BCR after radiotherapy had a nonnegligible risk of prostate cancer mortality. Improving risk stratification of patients with BCR is pivotal to guide salvage treatment decisions, reduce overtreatment, and limit the number of staging tests in the event of PSA elevations after primary treatment.

Salvage Stereotactic Reirradiation for Local Recurrence in the Prostatic Bed After Prostatectomy: A Retrospective Multicenter Study

BACKGROUND

Management of local recurrence of prostate cancer (PCa) in the prostatic bed after radical prostatectomy (RP) and radiotherapy remains challenging.

OBJECTIVE

To assess the efficacy and safety of salvage stereotactic body radiotherapy (SBRT) reirradiation in this setting and evaluate prognostic factors.

DESIGN, SETTING, AND PARTICIPANTS

We conducted a large multicenter retrospective series that included 117 patients who were treated with salvage SBRT for local recurrence in the prostatic bed after RP and radiotherapy in 11 centers across three countries.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Progression-free survival (PFS; biochemical, clinical, or both) was estimated using the Kaplan-Meier method. Biochemical recurrence was defined as prostate-specific antigen nadir +0.2 ng/ml, confirmed by a second increasing measure. The cumulative incidence of late toxicities was estimated using the Kalbfleisch-Prentice method by considering recurrence or death as a competing event.

RESULTS AND LIMITATIONS

The median follow-up was 19.5 mo. The median SBRT dose was 35 Gy. The median PFS was 23.5 mo (95% confidence interval [95% CI], 17.6-33.2). In the multivariable models, the volume of the recurrence and its contact with the urethrovesical anastomosis were significantly associated with PFS (hazard ratio [HR]/10 cm3 = 1.46; 95% CI, 1.08-1.96; p = 0.01 and HR = 3.35; 95% CI, 1.38-8.16; p = 0.008, respectively). The 3-yr cumulative incidence of grade ≥2 late GU or GI toxicity was 18% (95% CI, 10-26). In the multivariable analysis, a recurrence in contact with the urethrovesical anastomosis and D2% of the bladder were significantly associated with late toxicities of any grade (HR = 3.65; 95% CI, 1.61-8.24; p = 0.002 and HR/10 Gy = 1.88; 95% CI, 1.12-3.16; p = 0.02, respectively).

CONCLUSIONS

Salvage SBRT for local recurrence in the prostate bed may offer encouraging control and acceptable toxicity. Therefore, further prospective studies are warranted.

PATIENT SUMMARY

We found that salvage stereotactic body radiotherapy after surgery and radiotherapy allows for encouraging control and acceptable toxicity in locally relapsed prostate cancer.

Efficacy and Safety of Darolutamide in Patients with Nonmetastatic Castration-resistant Prostate Cancer Stratified by Prostate-specific Antigen Doubling Time: Planned Subgroup Analysis of the Phase 3 ARAMIS Trial

BACKGROUND

Patients with nonmetastatic castration-resistant prostate cancer (nmCRPC) have a high risk of progression to metastatic disease, particularly if their prostate-specific antigen doubling time (PSADT) is ≤6 mo. However, patients remain at a high risk with a PSADT of >6 mo.

OBJECTIVE

To evaluate the efficacy and safety of darolutamide versus placebo in patients stratified by PSADT >6 or ≤6 mo.

DESIGN, SETTING, AND PARTICIPANTS

A planned subgroup analysis of a global multicenter, double-blind, randomized, phase 3 trial in men with nmCRPC and PSADT ≤10 mo was conducted.

INTERVENTION

Patients were randomized 2:1 to oral darolutamide 600 mg twice daily or placebo, while continuing androgen-deprivation therapy.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The primary endpoint was metastasis-free survival (MFS). Secondary endpoints were overall survival (OS) and times to pain progression, first cytotoxic chemotherapy, and symptomatic skeletal events. Quality of life (QoL) was measured using validated prostate-relevant tools. Safety was recorded throughout the study.

RESULTS AND LIMITATIONS

Of 1509 patients enrolled, 469 had PSADT >6 mo (darolutamide n = 286; placebo n = 183) and 1040 had PSADT ≤6 mo (darolutamide n = 669; placebo n = 371). Baseline characteristics were balanced between subgroups. Darolutamide significantly prolonged MFS versus placebo in both subgroups (unstratified hazard ratio [95% confidence interval]: PSADT >6 mo, 0.38 [0.26-0.55]; PSADT ≤6 mo, 0.41 [0.33-0.52]). OS and other efficacy and QoL endpoints favored darolutamide with significant improvement over placebo in both subgroups. The incidence of adverse events, including events commonly associated with androgen receptor inhibitors (fractures, falls, hypertension, and mental impairment), and discontinuations due to adverse events were low and similar to placebo. Limitations include small subgroup populations.

CONCLUSIONS

In patients with nmCRPC and PSADT >6 mo (maximum 10 mo), darolutamide provided a favorable benefit/risk ratio, characterized by significant improvements in MFS, OS, and other clinically relevant endpoints; maintenance of QoL; and favorable tolerability.

PATIENT SUMMARY

In patients with prostate cancer that has stopped responding to standard hormonal therapy (indicated by an increase in prostate-specific antigen [PSA] levels), there is a risk that the cancer will spread to other parts of the body. This risk is highest when the time it takes for the PSA level to double (ie, "PSA doubling time" [PSADT]) is less than 6 mo. However, there is still a risk that the cancer will spread even if the PSADT is longer than 6 mo. In a group of patients whose PSADT was more than 6 mo but no more than 10 mo, treatment with darolutamide slowed the cancer spread and allowed them to live longer than patients who received placebo (inactive drug). Darolutamide treatment did not cause many side effects and helped maintain patients' quality of life without disruptions.

Postoperative Radiotherapy of Prostate Cancer: Adjuvant versus Early Salvage

Results of three randomized clinical trials (RCTs) comparing adjuvant radiotherapy (ART) and early salvage radiotherapy (eSRT) of prostate carcinoma and a subsequent meta-analysis of the individual patient data from these RCTs were recently published. The results suggest that early eSRT is as effective and potentially less toxic than ART. Therefore, eSRT should be considered the standard of care. However, due to limitations in the RCTs, ART remains a valid treatment option in patients with the combination of high-risk features such as Gleason Score (GS) 8–10, positive surgical margins (R1) and pathological T-stage 3 or 4 (pT3/4). This article provides a critical appraisal of the RCTs and the rationale for recommendations adopted in the current national guidelines regarding patients with high-risk features after radical prostatectomy (RP): ART should be offered in case of pT3/pT4 and R1 and Gleason Score 8–10; ART can be offered in case of pT3/pT4 and R0 and Gleason Score 8–10 as well as in case of multifocal R1 (including pT2) and Gleason Score 8–10. In any case, the alternative treatment option of eSRT in case of rising PSA should be discussed with the patient.