[18F]DCFPyL PET-MRI/CT for unveiling a molecularly defined oligorecurrent prostate cancer state amenable for curative-intent ablative therapy: study protocol for a phase II trial

Association of PSMA PET-derived Parameters and Outcomes of Patients Treated for Oligorecurrent Prostate Cancer

Background Prostate-specific membrane antigen (PSMA) PET is useful in the early detection of oligorecurrent prostate cancer (PCa), but whether PSMA PET parameters can be used to identify patients who would benefit from metastasis-directed therapy (MDT) with radiation or surgery remains uncertain. Purpose To assess the association of PSMA PET parameters with outcomes of patients with oligorecurrent PCa after MDT. Materials and Methods In this retrospective analysis of a single-center phase II trial that enrolled patients with biochemical recurrence of PCa after maximal local therapy and with no evidence of disease at conventional imaging, patients underwent PSMA PET (between May 2017 and November 2021), and unveiled recurrences were treated with MDT. Maximum standardized uptake value (SUVmax) and mean standardized uptake value (SUVmean) and PSMA tumor volume derived using thresholds of 2.5 (SUVmean2.5) and 41% (SUVmean41%), respectively, were recorded for sites of recurrence on PSMA PET scans, and a molecular imaging PSMA score was assigned. These parameters were also corrected for smooth filter and partial volume effects, and the PSMA score was reassigned. Cox proportional hazards models were used to evaluate the relationship between PSMA PET parameters and outcomes. Results A total of 74 men (mean age, 68.3 years ± 6.6 [SD]) with biochemical recurrence of PCa were included. PSMA PET revealed 145 lesions in the entire cohort, of which 125 (86%) were metastatic lymph nodes. Application of the correction factor changed the PSMA score in 88 of 145 lesions (61%). Mean SUVmax, SUVmean2.5, and SUVmean41% were associated with lower risk of biochemical progression (hazard ratio [HR] range, 0.77-0.95; 95% CI: 0.61, 1.00; P = .03 to P = .04). For corrected parameters, mean SUVmax, mean SUVmean2.5, mean SUVmean41%, mean PSMA score, maximum SUVmean2.5, maximum SUVmean41%, and maximum PSMA score were associated with a lower risk of biochemical progression (HR, 0.61-0.98; 95% CI: 0.39, 1.00; P = .01 to P = .04). Conclusion Measured and corrected PSMA PET parameters were associated with biochemical progression in men with oligorecurrent PCa treated with MDT. Clinical trial registration no. NCT03160794 © RSNA, 2023 See also the editorial by Civelek in this issue.

Oligometastasis in Prostate Cancer: Can We Learn from Those "Excluded" from a Phase 2 Trial?

We conducted and previously published a phase 2 trial of metastasis-directed therapy (MDT) in men with recurrence of prostate cancer at a low prostate-specific antigen level following radical prostatectomy and postoperative radiotherapy. All patients had negative conventional imaging and underwent prostate-specific membrane antigen (PSMA) positron emission tomography (PET). Patients without visible disease (n = 16) or with metastatic disease not amenable to MDT (n = 19) were excluded from the interventional study. The remaining patients with disease visible on PSMA-PET received MDT (n = 37). We analyzed all three groups to identify distinct phenotypes in the era of molecular imaging-based characterization of recurrent disease. Median follow up was 37 mo (interquartile range 27.5-43.0). There was no significant difference in time to the development of metastasis on conventional imaging among the groups; however, castrate-resistant prostate cancer-free survival was significantly shorter for patients with PSMA-avid disease not amenable to MDT (p = 0.047). Our findings suggest that PSMA-PET findings can help in discriminating diverging clinical phenotypes among men with disease recurrence and negative conventional imaging after local therapies with curative intent. There is a pressing need for better characterization of this rapidly growing population of patients with recurrent disease defined by PSMA-PET to derive robust selection criteria and outcome definitions for ongoing and future studies.

Patient summary

In men with prostate cancer with rising PSA levels following surgery and radiation, a newer type of scan called PSMA-PET (prostate-specific membrane antigen positron emission tomography) can be used to characterize and differentiate the patterns of recurrence, and inform future cancer outcomes.

18F-DCFPyL PET/CT for Initially Diagnosed and Biochemically Recurrent Prostate Cancer: Prospective Trial with Pathologic Confirmation

Background Prostate-specific membrane antigen (PSMA) PET is standard for newly diagnosed high-risk and biochemically recurrent (BCR) prostate cancer. Although studies suggest high specificity of 2-(3-{1-carboxy-5-[(6-[(18)F]fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid (DCFPyL) for targeting PSMA, false-positive findings have been identified and most studies lack histologic confirmation of malignancy. Purpose To estimate the positive predictive value (PPV) of DCFPyL PET/CT by providing histopathologic proof for DCFPyL-avid lesions suspected of being distant metastases at initial diagnosis and recurrence in BCR prostate cancer. Materials and Methods In this prospective trial, men with newly diagnosed high-risk prostate cancer (sample 1) or BCR prostate cancer and negative findings at conventional CT and/or bone scanning (sample 2) were enrolled between January and December 2021. All men underwent DCFPyL PET/CT. Suspected distant metastases and/or recurrences were biopsied. PPV was calculated. Results A total of 92 men with newly diagnosed prostate cancer (median age, 70 years; IQR, 64-75 years) (sample 1) and 92 men with BCR prostate cancer (median age, 71 years; IQR, 66-75 years) (sample 2) were enrolled. In sample 1, 25 of the 92 men (27%) demonstrated DCFPyL-avid lesions suspicious for distant metastases. Biopsy was performed in 23 of the 25 men (92%), with 17 of the 23 (74%) biopsies positive for malignancy and six (26%) benign. Of the six benign biopsies, three were solitary rib foci and three were solitary pelvic bone foci. In sample 2, 57 of the 92 men (62%) demonstrated DCFPyL-avid lesions suspicious for recurrence. Biopsy was performed in 37 of the 57 men (65%), with 33 of the 37 (89%) biopsies positive for malignancy and four (11%) benign. Of the four benign biopsies, two were subcentimeter pelvic nodes and/or nodules, one was a rib, and one was a pelvic bone focus. Conclusion PET/CT with 2-(3-{1-carboxy-5-[(6-[(18)F]fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid (DCFPyL) had a high biopsy-proven positive predictive value for distant metastases in newly diagnosed prostate cancer (74%) and for recurrence sites in men with biochemical recurrence (89%). However, there were DCFPyL-avid false-positive findings (particularly in ribs and pelvic bones). Solitary DCFPyL avidity in these locations should not be presumed as malignant. Biopsy may still be needed prior to therapy decisions. ClinicalTrials.gov registration no. NCT04700332 © RSNA, 2022 See also the editorial by Zukotynski and Kuo in this issue.

Extended Results and Independent Validation of a Phase 2 Trial of Metastasis Directed Therapy for Molecularly Defined Oligometastatic Prostate Cancer

PURPOSE

The role of metastasis-directed therapy (MDT) in molecularly defined oligorecurrent prostate cancer (PCa) remains irresolute. We present extended follow-up and an independent validation cohort of a prospective trial.

METHODS AND MATERIALS

This study consists of 2 sequential single-arm phase-2 trials of patients with biochemical recurrence (prostate specific antigen [PSA] 0.4-3.0 ng/mL) and negative conventional imaging after radical prostatectomy and postoperative radiation therapy. All patients underwent [¹⁸F]DCFPyL positron emission tomography/computed tomography. Patients with molecularly defined oligorecurrent prostate cancer underwent MDT with stereotactic body radiation therapy or surgery, without androgen deprivation therapy (ADT). The primary end point was biochemical response (≥50% PSA decline from baseline). Secondary end points included PSA progression-free survival and ADT-free survival. The sample size of 37 MDT patients was determined based on a Simon's 2-stage design with biochemical response rate >20%, and this design was also applied for the subsequent independent validation cohort.

RESULTS

Seventy-four patients underwent MDT: 37 each in the initial and validation cohorts. Both cohorts met the prespecified biochemical response rate and completed the planned 2-stages of accrual. For the pooled cohort, the median number of prostate specific membrane antigen positron emission tomography avid lesions was 2 and most (87%) recurrences were nodal. Sixty-four (87%) had stereotactic body radiation therapy and 10 (13%) had surgery. Median follow-up (interquartile range [IQR]) for the initial, validation and combined cohorts were 41 (35-46) months, 14 months (7-21), and 24 months (14-41), respectively. The biochemical response rates for the initial, validation and combined cohorts were 59%, 43%, and 51%, respectively. For the combined cohort, median biochemical progression-free survival was 21 months (95% confidence interval, 13-not reached), and median ADT-free survival was 45 months (95% confidence interval, 31-not reached).

CONCLUSIONS

Half of patients treated with MDT for molecularly defined-only oligorecurrent prostate cancer exhibited a biochemical response. This study provides necessary and validated evidence to support randomized trials aiming to determine whether MDT (alone or with systemic therapy) can affect clinically meaningful end points.

The future of PSMA PET and WB MRI as next-generation imaging tools in prostate cancer

Radiolabelled prostate-specific membrane antigen (PSMA)-based PET-CT has been shown in numerous studies to be superior to conventional imaging in the detection of nodal or distant metastatic lesions. ⁶⁸Ga-PSMA PET-CT is now recommended by many guidelines for the detection of biochemically relapsed disease after radical local therapy. PSMA radioligands can also function as radiotheranostics, and Lu-PSMA has been shown to be a potential new line of treatment for metastatic castration-resistant prostate cancer. Whole-body (WB) MRI has been shown to have a high diagnostic performance in the detection and monitoring of metastatic bone disease. Prospective, randomized, multicentre studies comparing ⁶⁸Ga-PSMA PET-CT and WB MRI for pelvic nodal and metastatic disease detection are yet to be performed. Challenges for interpretation of PSMA include tracer trapping in non-target tissues and also urinary excretion of tracers, which confounds image interpretation at the vesicoureteral junction. Additionally, studies have shown how long-term androgen deprivation therapy (ADT) affects PSMA expression and could, therefore, reduce tracer uptake and visibility of PSMA⁺ lesions. Furthermore, ADT of short duration might increase PSMA expression, leading to the PSMA flare phenomenon, which makes the accurate monitoring of treatment response to ADT with PSMA PET challenging. Scan duration, detection of incidentalomas and presence of metallic implants are some of the major challenges with WB MRI. Emerging data support the wider adoption of PSMA PET and WB MRI for diagnosis, staging, disease burden evaluation and response monitoring, although their relative roles in the standard-of-care management of patients are yet to be fully defined.

[18F]DCFPyL PET/CT in detection and localization of recurrent prostate cancer following prostatectomy including low PSA < 0.5 ng/mL

PURPOSE

The primary aim of this retrospective multicenter analysis was to assess the performance of PSMA PET/CT using [18F]DCFPyL in the detection and localization of recurrent prostate cancer post radical prostatectomy (RP). Particular reference is given to low PSA groups < 0.5 ng/mL to aid discussion around the inclusion of this group in PSMA guidelines and funding pathways.

METHODS

Retrospective analysis of combined PSMA database patients from centers in Australia and New Zealand. Two hundred twenty-two patients presenting with recurrence post RP were stratified into five PSA groups (ng/mL): 0-0.19, 0.2-0.49, 0.5-0.99, 1-1.99, and ≥ 2. Lesions detected by [18F]DCFPyL PET/CT were recorded as local recurrence, locoregional nodes, and metastases.

RESULTS

Of 222 patients, 155 (69.8%) had evidence of abnormal uptake suggestive of recurrent prostate cancer. The detection efficacies for [18F]DCFPyL PET/CT were 91.7% (44/48) for PSA levels ≥ 2 ng/mL, 82.1% (23/28) for PSA levels 1-1.99 ng/mL, 62.8% (27/43) for PSA levels 0.5-0.99 ng/mL, 58.7% (54/92) for PSA levels 0.2-0.49 ng/mL, and 63.6% (7/11) for PSA levels ≤ 0.2 ng/mL. In those with PSA < 0.5 ng/mL, 47.6% (49/103) had detectable lesions, 71.4% (35/49) had disease confined to the pelvis, 22.4% (11/49) had prostate bed recurrence, 49.0% (24/49) had pelvic lymph nodes, and 28.6% (14/49) had extra pelvic disease.

CONCLUSION

[18F]DCFPyL PET/CT has a high detection rate in recurrence following RP even at low PSA levels with similar detection levels in the PSA subgroups < 0.5 ng/mL. Employing rigid PSA thresholds when constructing guidelines for PSMA PET/CT funding eligibility may result in a significant number of patients below such thresholds having delayed or inappropriate treatment.

Positron Emission Tomography and Whole-body Magnetic Resonance Imaging for Metastasis-directed Therapy in Hormone-sensitive Oligometastatic Prostate Cancer After Primary Radical Treatment: A Systematic Review

CONTEXT

Next-generation imaging includes positron emission tomography (PET) imaging and whole-body magnetic resonance imaging (wbMRI) including diffusion-weighted imaging. Accurate quantification of oligometastatic disease using next-generation imaging is important to define the role and value of metastasis-directed therapy (MDT).

OBJECTIVE

To perform a review of next-generation imaging modalities in the detection of recurrent oligometastatic hormone-sensitive prostate cancer in men who received prior radical treatment for localized disease.

EVIDENCE ACQUISITION

MEDLINE, Scopus, Cochrane Libraries, and Web of Science databases were systematically searched for studies reporting next-generation imaging and oncological outcomes. An expert panel of urologists, radiation oncologists, radiologists, and nuclear medicine physicians performed a nonsystematic review of strengths and limitations of currently available imaging options for detecting the presence and extent of recurrent oligometastatic disease.

EVIDENCE SYNTHESIS

From 370 articles identified, three clinical trials and 21 observational studies met the following inclusion criteria: metachronous oligometastatic recurrence after radical treatment for prostate cancer, MDT, and hormone-sensitive patients. Androgen deprivation therapy (ADT) was allowed before MDT. Next-generation imaging modalities included PET/computed tomography and/or PET/MRI with the following tracers: choline (n = 1), NaF (n = 1), and prostate-specific membrane antigen (PSMA; n = 1) for clinical trials; choline (n = 7) or PSMA (n = 11) or both (n = 3) for observational studies. The number of metastases ranged from two to five lesions in most studies. In PSMA-based studies, progression-free survival ranged from 19% to 100%, whereas in studies employing choline, progression-free survival ranged from 16% to 93%. Overall, ADT-free survival ranged from 48% to 79%, while local control was reported as 75-100% and prostate-specific antigen response as 23-94%. Among the different PET tracers and wbMRI, PSMA PET is emerging as the most accurate imaging technique in defining the oligometastatic status.

CONCLUSIONS

PSMA and choline PET contribute to guiding MDT in men with hormone-sensitive oligometastatic prostate cancer. Further studies are warranted to ascertain their role and optimize the timing of imaging for such patients.

PATIENT SUMMARY

We looked at the evidence regarding the use of modern imaging techniques to direct additional treatments in men with early spread of prostate cancer after they receive their initial radical treatment. We found that next-generation imaging, in particular prostate-specific membrane antigen and choline positron emission tomography, can successfully guide metastasis-directed therapies, and further trials should evaluate which modalities are best suited to improve outcomes for our patients.

Curative-intent Metastasis-directed Therapies for Molecularly-defined Oligorecurrent Prostate Cancer: A Prospective Phase II Trial Testing the Oligometastasis Hypothesis

BACKGROUND

The hypothesis of a curable oligometastatic prostate cancer (PCa) state remains to be clinically-proven. Conventional imaging often fails to localize early recurrences, hampering the potential for radical approaches.

OBJECTIVE

We hypothesize that prostate-specific membrane antigen (PSMA)-targeted PET-MR/CT allows for earlier detection and localization of oligorecurrent-PCa, unveiling a molecularly-defined state amenable to curative-intent metastasis-directed treatment (MDT).

DESIGN/SETTING/PARTICIPANTS

Single-institution single-arm phase-two study. Patients with rising PSA (0.4-3.0 ng/mL) after maximal local therapy (radical prostatectomy and post-operative radiotherapy), negative conventional staging, and no prior salvage hormonal therapy (HT) were eligible.

INTERVENTIONS

All patients underwent [¹⁸F]DCFPyL PET-MR/CT. Patients with molecularly-defined oligorecurrent-PCa had MDT (stereotactic ablative body radiotherapy [SABR] or surgery) without HT.

OUTCOME MEASUREMENTS/STATISTICAL ANALYSIS

Primary endpoint was biochemical response (complete, i.e. biochemical 'no evidence of disease' [bNED], or partial response [100% or ≥50% PSA decline from baseline, respectively]) after MDT. Simon's two-stage design was employed (null and alternate hypotheses <5% and >20% response rate, respectively), with α and β of 0.1.

RESULTS

Seventy-two patients were enrolled (May/2017-July/2019). Thirty-eight (53%) had PSMA-detected oligorecurrent-PCa amenable for MDT. Thirty-seven (51%) agreed to MDT: 10 and 27 underwent surgery and SABR, respectively. Median follow-up was 15.9 months (IQR 9.8-19.1). Of patients receiving MDT, the overall response rate was 60%, including 22% rendered bNED. One (2.7%) grade 3 toxicity (intra-operative ureteric injury) was observed.

CONCLUSIONS

PSMA-defined oligorecurrent-PCa can be rendered bNED, a necessary step towards cure, in 1 of 5 patients receiving MDT alone. Randomized trials are justified to determine if MDT +/- systemic agents can expand the curative therapeutic armamentarium for PCa.

PATIENT SUMMARY

We studied men treated for prostate cancer with rising PSA. We found PSMA imaging detected recurrent cancer in three-quarters of patients, and targeted treatment to these areas significantly decreased PSA in half of patients.