Evolving Role of Prostate-Specific Membrane Antigen-Positron Emission Tomography in Metastatic Hormone-Sensitive Prostate Cancer: More Questions than Answers?

A prospective study on the early evaluation of response to androgen receptor-targeted agents with 11C-Choline, 68Ga-PSMA, and 18F-FACBC PET in metastatic castration-resistant prostate cancer: a single-center experience

BACKGROUND

The early identification of responsive and resistant patients to androgen receptor-targeting agents (ARTA) in metastatic castration-resistant prostate cancer (mCRPC) is not completely possible with prostate-specific antigen (PSA) assessment and conventional imaging. Considering its ability to determine metabolic activity of lesions, positron emission tomography (PET) assessment might be a promising tool.

PATIENTS AND METHODS

We carried out a monocentric prospective study in patients with mCRPC treated with ARTA to evaluate the role of different PET radiotracers: 49 patients were randomized to receive 11C-Choline, Fluorine 18 fluciclovine (anti-1-amino-3-18F-fluorocyclobutane-1-carboxylic acid - FACBC) (18F-FACBC), or Gallium-68-prostate-specific-membrane-antigen (68Ga-PSMA) PET, one scan before therapy and one 2 months later. The primary aim was to investigate the performance of three novel PET radiotracers for the early evaluation of response to ARTA in metastatic CRPC patients; the outcome evaluated was biochemical response (PSA reduction ≥50%). The secondary aim was to investigate the prognostic role of several semiquantitative PET parameters and their variations with the different radiotracers in terms of biochemical progression-free survival (bPFS) and overall survival (OS). The study was promoted by the Italian Department of Health (code RF-2016-02364809).

RESULTS

Regarding the primary endpoint, at log-rank test a statistically significant correlation was found between metabolic tumor volume (MTV) (P = 0.018) and total lesion activity (TLA) (P = 0.025) percentage variation among the two scans with 68Ga-PSMA PET and biochemical response. As for the secondary endpoints, significant correlations with bPFS were found for 68Ga-PSMA total MTV and TLA at the first scan (P = 0.001 and P = 0.025, respectively), and MTV percentage variation (P = 0.031). For OS, statistically significant correlations were found for different 68Ga-PSMA and 18F-FACBC parameters and for major maximum standardized uptake value at the first 11C-Choline PET scan.

CONCLUSIONS

Our study highlighted that 11C-Choline, 68Ga-PSMA, and 18F-FACBC semiquantitative PET parameters and their variations present a prognostic value in terms of OS and bPFS, and MTV and TLA variations with 68Ga-PSMA PET a correlation with biochemical response, which could help to assess the response to ARTA.

Validation of metastasis-free survival as a surrogate endpoint for overall survival in localized prostate cancer in the era of docetaxel for castration-resistant prostate cancer

BACKGROUND

Prior work from the Intermediate Clinical Endpoints in Cancer of the Prostate (ICECaP) consortium (ICECaP-1) demonstrated that metastasis-free survival (MFS) is a valid surrogate for overall survival (OS) in localized prostate cancer (PCa). This was based on data from patients treated predominantly before 2004, prior to docetaxel being available for the treatment of metastatic castrate-resistant prostate cancer (mCRPC). We sought to validate surrogacy in a more contemporary era (ICECaP-2) with greater availability of docetaxel and other systemic therapies for mCRPC.

PATIENTS AND METHODS

Eligible trials for ICECaP-2 were those providing individual patient data (IPD) after publication of ICECaP-1 and evaluating adjuvant/salvage therapy for localized PCa, and which collected MFS and OS data. MFS was defined as distant metastases or death from any cause, and OS was defined as death from any cause. Surrogacy was evaluated using a meta-analytic two-stage validation model, with an R2 ≥ 0.7 defined a priori as clinically relevant.

RESULTS

A total of 15 164 IPD from 14 trials were included in ICECaP-2, with 70% of patients treated after 2004. The median follow-up was 8.3 years and the median postmetastasis survival was 3.1 years in ICECaP-2, compared with 1.9 years in ICECaP-1. For surrogacy condition 1, Kendall's tau was 0.92 for MFS with OS at the patient level, and R2 from weighted linear regression (WLR) of 8-year OS on 5-year MFS was 0.73 (95% confidence interval 0.53-0.82) at the trial level. For condition 2, R2 was 0.83 (95% confidence interval 0.64-0.89) from WLR of log[hazard ratio (HR)]-OS on log(HR)-MFS. The surrogate threshold effect on OS was an HR(MFS) of 0.81.

CONCLUSIONS

MFS remained a valid surrogate for OS in a more contemporary era, where patients had greater access to docetaxel and other systemic therapies for mCRPC. This supports the use of MFS as the primary outcome measure for ongoing adjuvant trials in localized PCa.

Metastatic Hormone-Sensitive Prostate Cancer in the Era of Doublet and Triplet Therapy

OPINION STATEMENT

Treatment for metastatic hormone-sensitive prostate cancer has undergone significant evolution in recent years, leading to substantial improvements in overall survival. Men are living longer than ever before with a median survival now which is almost 6 years. The timing and extent of metastatic disease combined with individual patient factors helps treatment recommendation of doublet therapy including androgen deprivation (ADT) plus either chemotherapy or androgen receptor signaling inhibition (ARSI) or triplet therapy with ADT+ARSI+chemotherapy. New treatments must continue to be developed to enhance survival with goals of cure. Better biomarkers that allow for more effective treatments will enhance disease control, quality of life, and survival.

PSMA guided approach for bIoCHEmical relapse after prostatectomy- (PSICHE) trial (NCT05022914). Detection rate and treatment decision after 68Ga-PSMA PET/CT within a prospective study

BACKGROUND

Ultrasensitive imaging has been demonstrated to influence biochemical relapse treatment. PSICHE is a multicentric prospective study, aimed at exploring detection rate with 68Ga-PSMA-11 positron emission tomography/computed tomography (PET/CT) and outcomes with a predefined treatment algorithm tailored to the imaging.

METHODS

Patients affected by biochemical recurrence after surgery (prostate specific antigen [PSA] > 0.2 < 1 ng/mL) underwent staging with 68Ga-PSMA PET/CT. Management followed this treatment algorithm accordingly with PSMA results: prostate bed salvage radiotherapy (SRT) if negative or positive within prostate bed, stereotactic body radiotherapy (SBRT) if pelvic nodal recurrences or oligometastatic disease, androgen deprivation therapy (ADT) if nonoligometastatic disease. Chi-square test was used to evaluate the relationship between baseline features and rate of positive PSMA PET/CT.

RESULTS

One hundred patients were enrolled. PSMA results were negative/positive in the prostate bed in 72 patients, pelvic nodal or extrapelvic metastatic disease were detected in 23 and 5 patients. Twenty-one patients underwent observation because of prior postoperative radiotherapy (RT)/treatment refusal. Fifty patients were treated with prostate bed SRT, 23 patients underwent SBRT to pelvic nodal disease, five patients were treated with SBRT to oligometastatic disease. One patient underwent ADT. NCCN high-risk features, stage > pT3 and ISUP score >3 reported a significantly higher rate of positive PSMA PET/CT after restaging (p = 0.01, p = 0.02, and p = 0.002). By quartiles of PSA, rate of positive PSMA PET/CT was 26.9% (>0.2; <0.29 ng/mL), 24% (>0.3; <0.37 ng/mL), 26.9% (>0.38; <0.51 ng/mL), and 34.7% (>0. 52; <0.98 ng/mL).

CONCLUSIONS

PSICHE trial constitute a useful platform to collect data within a clinical framework where modern imaging and metastasis-directed therapy are integrated.

Personalizing approaches to the management of metastatic hormone sensitive prostate cancer: role of advanced imaging, genetics and therapeutics

PURPOSE

To summarize contemporary and emerging strategies for the diagnosis and management of metastatic hormone sensitive prostate cancer (mHSPC), focusing on diagnostic testing and therapeutics.

METHODS

Literature review using PUBMED-Medline databases as well as clinicaltrials.gov to include reported or ongoing clinical trials on treatment for mHSPC. We prioritized the findings from phase III randomized clinical trials, systematic reviews, meta-analyses and clinical practice guidelines.

RESULTS

There have been significant changes to the diagnosis and staging evaluation of mHSPC with the integration of increasingly accurate positron emission tomography (PET) imaging tracers that exceed the performance of conventional computerized tomography (CT) and bone scan. Germline multigene testing is recommended for the evaluation of patients newly diagnosed with mHSPC given the prevalence of actionable alterations that may create candidacy for specific therapies. Although androgen deprivation therapy (ADT) remains the backbone of treatment for mHSPC, approaches to first-line treatment include the integration of multiple agents including androgen receptor synthesis inhibitors (ARSI; abiraterone) Androgen Receptor antagonists (enzalutamide, darolutamide, apalautamide), and docetaxel chemotherapy. The combination of ADT, ARSI, and docetaxel chemotherapy has recently been evaluated in a randomized trial and was associated with significantly improved overall survival including in patients with a high burden of disease. The role of local treatment to the prostate with radiation has been evaluated in randomized trials with additional studies underway evaluating the role of cytoreductive radical prostatectomy.

CONCLUSION

The staging and initial management of patients with mHSPC has undergone significant advances in the last decade with advancements in the diagnosis, treatment and sequencing of therapies.

What is the ideal combination therapy in de novo, oligometastatic, castration-sensitive prostate cancer?

PURPOSE

To review current evidence regarding the management of de novo, oligometastatic, castration-sensitive prostate cancer (PCa).

METHODS

A literature search was conducted on PubMed/Medline and a narrative synthesis of the evidence was performed in August 2022.

RESULTS

Oligometastatic disease is an intermediate state between localized and aggressive metastatic PCa defined by ≤ 3-5 metastatic lesions, although this definition remains controversial. Conventional imaging has limited accuracy in detecting metastatic lesions, and the implementation of molecular imaging could pave the way for a more personalized treatment strategy. However, oncological data supporting this strategy are needed. Radiotherapy to the primary tumor should be considered standard treatment for oligometastatic PCa (omPCa). However, it remains to be seen whether local therapy still has an additional survival benefit in patients with de novo omPCa when treated with the most modern systemic therapy combinations. There is insufficient evidence to recommend cytoreductive radical prostatectomy as local therapy; or stereotactic body radiotherapy as metastasis-directed therapy in patients with omPCa. Current data support the use of intensified systemic therapy with androgen deprivation therapy (ADT) and next-generation hormone therapies (NHT) for patients with de novo omPCa. Docetaxel has not demonstrated benefit in low volume disease. There are insufficient data to support the use of triple therapy (i.e., ADT + NHT + Docetaxel) in low volume disease.

CONCLUSION

The present review discusses current data in de novo, omPCa regarding its definition, the increasing role of molecular imaging, the place of local and metastasis-directed therapies, and the intensification of systemic therapies.

Future directions in systemic treatment of metastatic hormone-sensitive prostate cancer

The landscape of advanced prostate cancer treatment has evolved tremendously in past decades. The treatment paradigm has shifted from androgen deprivation therapy (ADT) alone to doublet combinations comprising ADT with docetaxel or an androgen receptor inhibitor, and now triplet therapy involving all 3 classes of agents. Robust clinical data has demonstrated survival benefits with this strategy of upfront treatment intensification. Subgroup analysis has alluded to the importance of tailoring treatment according to metastatic disease burden. However, defining the volume of disease is becoming increasingly controversial due to the advent of next generation molecular imaging. Several trials testing established agents in the castrate-resistant setting are now underway in metastatic hormone sensitive prostate cancer patients. As the treatment milieu is enriched earlier in the disease trajectory, future studies should elucidate biomarkers to further define specific patient populations who will benefit most from treatment intensification and/or de-escalation, with what agents and for what duration.

Philosophy of Cancer Theranostics

Imagine a theranostic nuclear physician oncologist engaged in a Socratic philosophic dialogue. Questions that may be posed include the status of our current knowledge base of radiomolecular tumor biology, the meaning of precision in personalized dosimetry, the nature of responsibility for direct patient care, and the moral and ethical dimensions of individual quality of life (QOL) when survival is prolonged. This review invites reflective enquiry into one's personal practice of theranostics in cancer care, with the objective of optimizing clinical outcomes, not only in terms of prolonged survival but also individual QOL, in respect of its meaning for each patient, both physically and emotionally.

Rates of Positive Abdominal Computed Tomography and Bone Scan Findings Among Men with Cambridge Prognostic Group 4 or 5 prostate cancer: A Nationwide Registry Study

European and American guidelines recommend abdominal computed tomography (CT) and bone scans for staging of high-risk prostate cancer (PC). To improve clinical risk stratification of nonmetastatic PC a new, five-tier risk classification system has been developed, the Cambridge Prognostic Groups (CPG), in which “high-risk” PC is divided into favourable CPG 4 and unfavourable CPG 5. We used the National Prostate Cancer Register of Sweden (NPCR) to define the rates of positive CT and bone scan findings among men with CPG 4 or 5 cancer. Among men with CPG 4 and prostate-specific antigen (PSA) <50 ng/ml, only 3.6% (95% confidence interval 2.9–4.5%) of the CT scans showed regional lymph-node metastasis (N1M0), while 6.2% (95% confidence interval 5.4–7.0%) of the bone scans were positive. Rates for both were higher in the subgroups with PSA 50–99 ng/ml (10% and 15%) and with CPG 5 disease. The low positivity rate questions routine use of CT for men with CPG 4 cancer and PSA <50 ng/ml, particularly considering the poor sensitivity and specificity for detection of lymph node metastasis. The positivity rate was higher for bone scans, and as current clinical practice relies on trials using bone scans for staging (eg, to define low- versus high-volume metastatic disease), continued routine use of bone scans seems justified.

Patient summary

Our analysis of data from the National Prostate Cancer Register of Sweden showed that for men with favourable high-risk prostate cancer (Cambridge Prognostic Group 4), the rate of positive computed tomography (CT) scans was low. This result suggests that CT scans may not be necessary for detecting cancer spread in men with Cambridge Prognostic Group 4 prostate cancer .