Impact of 68Ga-PSMA-11 PET/CT on the Management of Prostate Cancer Patients with Biochemical Recurrence

68Ga-PSMA PET/CT in prostate cancer patients - patterns of disease, benign findings and pitfalls

Background

68Ga-PSMA PET/CT has an important role in assessment of prostate cancer patients with biochemical recurrence and is evolving in staging high- and intermediate risk disease. The aim of present study was to describe the metastatic patterns and frequency of involved sites of prostate cancer and to assess the incidence of benign Ga68-PSMA avid PET/CT findings in a large patient population.

Methods

68Ga-PSMA PET/CT studies performed in two tertiary medical centers over a period of 24 months were retrospectively reviewed. The incidence and location of pathological 68Ga-PSMA avid foci, suspicious to represent malignancy, as well as those of unexpected benign foci of increased 68Ga-PSMA activity were documented and analyzed.

Results

There were 445 68Ga-PSMA studies in 438 men (mean age 72.4, range 51–92 years) with prostate cancer referred for biochemical failure (n = 270, 61%), staging high-risk disease (n = 112, 25%), response assessment (n = 30, 7%), follow-up (n = 22, 5%) and suspected bone metastases (n = 11, 2%). 68Ga-PSMA avid disease sites were observed in 319 studies (72%), in 181 studies (67%) for biochemical recurrence, 94 studies for staging (84%) (p < 0.05), in 22 studies for response assessment (73%), 10 follow up studies (45%) and in five patients with suspected bone metastases (45%). 68Ga-PSMA avid lesions were most commonly detected in the prostate (n = 193, 43%), loco-regional spread (n = 51, 11%), abdomino-pelvic nodes (n = 129, 29%) and distant metastases (n = 158, 36%), including bone metastases (n = 11, 25%), distant lymphadenopathy (n = 29, 7%) and other organs (n = 18, 4%). Distant 68Ga-PSMA-avid metastases were commonly seen in patients with biochemical recurrence (14/21 lesions), but were not seen in patient referred for staging (p < 0.013). There were 96 non-malignant 68Ga-PSMA avid foci in 81 studies, most common in reactive lymph nodes (n = 36, 38%), nonmalignant bone lesions (n = 21, 22%), thyroid nodules (n = 9, 9%), ganglions (n = 9, 9%) and lung findings (n = 8, 8%).

Conclusion

The distribution of 68Ga-PSMA avid metastatic lesions is similar to data previously reported mainly from autopsy with comparable detection rates, indicating 68Ga-PSMA PET/CT is an accurate detection tool in patients with metastatic prostate cancer. If confirmed by further prospective studies 68Ga-PSMA PET/CT should be included in the guidelines to evaluate disease extent in these patients.

Clinical significance and predictors of oncologic outcome after radical prostatectomy for invisible prostate cancer on multiparametric MRI

Background

The objective of our study was to evaluate the clinical significance of invisible prostate cancer (iPCa) on multiparametric magnetic resonance imaging (mpMRI) by analyzing clinical parameters and oncologic outcomes.

Methods

We retrospectively reviewed the records of patients treated with radical prostatectomy (RP) from 2010 to 2015 at our institution. Before RP, all patients were confirmed to have prostate cancer based on prostate biopsy. We excluded patients who underwent neoadjuvant therapy. Additionally, we excluded patients who had incomplete mpMRI based on PI-RADS (Prostate Imaging Reporting and Data System). iPCa was defined as having no grade 3 or higher region of interests using a scoring system established by PI-RADS without limitations on interpretation from mpMRI by radiologists. We selected patients with iPCa using this protocol. We analyzed data using univariate and multivariate cox regression analysis, logistic analysis, Kaplan-Meier curves, and receiver operator characteristic curves to predict biochemical recurrence (BCR).

Results

A total of 213 patients with iPCa were selected according to the patient selection protocol. Among them, pathological findings showed that Gleason score (GS) G6, G7 and ≥ G8 were present in 115 cases (54.0%), 78 cases (36.6%), and 20 cases (9.4%), respectively. Further, extracapsular extension (ECE), positive surgical margins (PSM), and lymphovascular invasion (LVI) were present in 28 (13.1%), 18 (8.5%), and 3 cases (1.4%), respectively. Seminal vesicle invasion (SVI) was observed in one case (0.5%). During a median follow-up time of 51 months, BCR was observed 29 cases. Adverse pathology (AP) was defined as GS ≥8, ECE, SVI and LVI. AP and prostate specific antigen (PSA) were significantly associated with BCR. Moreover, PSA > 6.2 ng/ml was suggested as a cut-off value for predicting BCR.

Conclusions

In our results, cases of iPCa had clinically significant PCa, and AP and poor prognosis were also observed in some. Additionally, we found that PSA is the most clinically reliable predictor of oncologic outcome. We suggest that active treatment and diagnosis should be considered for patients with iPCa with PSA > 6.2 ng/ml.

Meeting report from the Prostate Cancer Foundation PSMA-directed radionuclide scientific working group

INTRODUCTION

The Prostate Cancer Foundation (PCF) convened a PSMA-Directed Radionuclide Scientific Working Group on November 14, 2017, at Weill Cornell Medicine, New York, NY.

METHODS

The meeting was attended by 35 global investigators with expertise in prostate cancer biology, radionuclide therapy, molecular imaging, prostate-specific membrane antigen (PSMA)-targeted agents, drug development, and prostate cancer clinical trials. The goal of this meeting was to discuss the potential for using PSMA-targeted radionuclide agents for the treatment of advanced prostate cancer and to define the studies and clinical trials necessary for validating and optimizing the use of these agents.

RESULTS

Several major topic areas were discussed including the overview of PSMA biology, lessons and applications of PSMA-targeted PET imaging, the nuances of designing PSMA-targeted radionuclide agents, clinical experiences with PSMA-targeted radionuclides, PCF-funded projects to accelerate PSMA-targeted radionuclide therapy, and barriers to the use of radionuclide treatments in widespread clinical practice.

DISCUSSION

This article reviews the major topics discussed at the meeting with the goal of promoting research that will validate and optimize the use of PSMA-targeted radionuclide therapies for the treatment of advanced prostate cancer.

Outcome after PSMA PET/CT based salvage radiotherapy in patients with biochemical recurrence after radical prostatectomy: a bi-institutional retrospective analysis

Prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT) detects prostate cancer recurrence at low PSA levels. Radiotherapy with dose escalation to the former prostate bed has been associated with improved biochemical recurrence-free survival (BRFS). Thus, we hypothesized that PSMA PET/CT-guided salvage radiotherapy leads to improved BRFS. Methods: A total of 204 consecutive patients were referred for salvage radiotherapy following radical prostatectomy. PSMA PET/CT scans were performed and patients with PSA persistence (109 patients) or evidence of distant metastases (5 patients) were excluded from this analysis. Thus, the following analysis is based on a total of 90 patients who underwent PSMA PET/CT prior to radiotherapy due to biochemical recurrence and received salvage radiotherapy. In case of PET-positive findings, antiandrogen therapy was commenced before initiation of radiotherapy. BRFS (PSA ≤ 0.2 ng/ml) was defined as the study endpoint. Results: PET-positive lesions were detected in 42/90 (47%) patients: 24/42 (27%) fossa recurrence only, 12/42 (13%) pelvic lymph nodes only and 6/42 (7%) fossa and pelvic lymph node recurrence. Median PSA before radiotherapy was 0.44 (0.11 - 6.24). Cumulatively, a total dose of 70.0 Gy (67.2 - 72 Gy) was delivered to local macroscopic tumor, 66 Gy (59.4 - 70.2 Gy) to the prostatic fossa, 60.8 Gy (54 - 66 Gy) to PET-positive lymph nodes and 50.4 Gy (45 - 50.4 Gy) to the lymphatic pathways. After a median follow-up of 23 months, BRFS was 78%. Antiandrogen therapy was ongoing in 4 patients at last follow-up. No significant difference in BRFS between PET-positive (74%) vs. PET-negative patients (82%; p>0.05) was observed at last follow-up. Two patients had late genitourinary toxicity grade 3 and no patient had gastrointestinal toxicity ≥ 3 (NCI-CTCAE v4.03). Conclusion: PSMA PET/CT-guided salvage radiotherapy is an effective and safe local treatment option. No difference in BRFS between PET-positive and PET-negative patients was observed, indicating effective targeting of PET-positive lesions. PSMA PET/CT when readily available should be offered to patients with PSA recurrence for treatment individualization.

Imaging Prostate Cancer With Prostate-Specific Membrane Antigen PET/CT and PET/MRI: Current and Future Applications

OBJECTIVE

The purpose of this article is to describe the large number of radiotracers being evaluated for prostate-specific membrane antigen (PSMA) PET, which is becoming a central tool in the staging of prostate cancer.

CONCLUSION

PSMA PET is a highly promising modality for the staging of prostate cancer because of its higher detection rate compared with that of conventional imaging. Both PET/CT and PET/MRI offer benefits with PSMA radiotracers, and PSMA PET findings frequently lead to changes in management. It is imperative that subsequent treatment changes be evaluated to show improved outcomes. PSMA PET also has potential applications, including patient selection for PSMA-based radioligand therapy and evaluation of treatment response.

Scandium and terbium radionuclides for radiotheranostics: current state of development towards clinical application

Currently, different radiometals are in use for imaging and therapy in nuclear medicine: ⁶⁸Ga and ¹¹¹In are examples of nuclides for positron emission tomography (PET) and single photon emission computed tomography (SPECT), respectively, while ¹⁷⁷Lu and ²²⁵Ac are used for β⁻- and α-radionuclide therapy. The application of diagnostic and therapeutic radionuclides of the same element (radioisotopes) would utilize chemically-identical radiopharmaceuticals for imaging and subsequent treatment, thereby enabling the radiotheranostic concept. There are two elements which are of particular interest in this regard: Scandium and Terbium. Scandium presents three radioisotopes for theranostic application. ⁴³Sc (T_1/2 = 3.9 h) and ⁴⁴Sc (T_1/2 = 4.0 h) can both be used for PET, while ⁴⁷Sc (T_1/2 = 3.35 d) is the therapeutic match—also suitable for SPECT. Currently, ⁴⁴Sc is most advanced in terms of production, as well as with pre-clinical investigations, and has already been employed in proof-of-concept studies in patients. Even though the production of ⁴³Sc may be more challenging, it would be advantageous due to the absence of high-energetic γ-ray emission. The development of ⁴⁷Sc is still in its infancy, however, its therapeutic potential has been demonstrated preclinically. Terbium is unique in that it represents four medically-interesting radioisotopes. ¹⁵⁵Tb (T_1/2 = 5.32 d) and ¹⁵²Tb (T_1/2 = 17.5 h) can be used for SPECT and PET, respectively. Both radioisotopes were produced and tested preclinically. ¹⁵²Tb has been the first Tb isotope that was tested (as ¹⁵²Tb-DOTATOC) in a patient. Both radionuclides may be of interest for dosimetry purposes prior to the application of radiolanthanide therapy. The decay properties of ¹⁶¹Tb (T_1/2 = 6.89 d) are similar to ¹⁷⁷Lu, but the coemission of Auger electrons make it attractive for a combined β⁻/Auger electron therapy, which was shown to be effective in preclinical experiments. ¹⁴⁹Tb (T_1/2 = 4.1 h) has been proposed for targeted α-therapy with the possibility of PET imaging. In terms of production, ¹⁶¹Tb and ¹⁵⁵Tb are most promising to be made available at the large quantities suitable for future clinical translation. This review article is dedicated to the production routes, the methods of separating the radioisotopes from the target material, preclinical investigations and clinical proof-of-concept studies of Sc and Tb radionuclides. The availability, challenges of production and first (pre)clinical application, as well as the potential of these novel radionuclides for future application in nuclear medicine, are discussed.

PSMA-PET based radiotherapy: a review of initial experiences, survey on current practice and future perspectives

⁶⁸Gallium prostate specific membrane antigen (PSMA) ligand positron emission tomography (PET) is an increasingly used imaging modality in prostate cancer, especially in cases of tumor recurrence after curative intended therapy. Owed to the novelty of the PSMA-targeting tracers, clinical evidence on the value of PSMA-PET is moderate but rapidly increasing. State of the art imaging is pivotal for radiotherapy treatment planning as it may affect dose prescription, target delineation and use of concomitant therapy.

This review summarizes the evidence on PSMA-PET imaging from a radiation oncologist’s point of view. Additionally a short survey containing twelve examples of patients and 6 additional questions was performed in seven mayor academic centers with experience in PSMA ligand imaging and the findings are reported here.

Current application and future perspectives of prostate specific membrane antigen PET imaging in prostate cancer

As precision medicine evolves, the contribution of molecular imaging to the management of prostate cancer (PCa) patients, especially for positron-emission tomography (PET) imaging, is gaining importance. Highly successful approaches to measure the expression of the prostate specific membrane antigen (PSMA) have been introduced recently. PSMA, the glutamate carboxypeptidase II, is a membrane bound metallo-peptidase that is overexpressed in 90-100% of PCa cells. Due to its selective over-expression, PSMA is a reliable tissue marker for prostate cancer and is considered an ideal target for tumor specific imaging and therapy. A variety of PET and SPECT probes targeting this peptide receptor have been introduced. These are undergoing extensive clinical evaluations. Initial results attest to a high accuracy for disease detection compared conventional radiology (CT or MRI) and other nuclear medicine procedure (choline PET or fluciclovine PET). However, prospective evaluation of the impact on patient management for PSMA-ligand PET and its impact on patient outcome is currently missing. Finally, PSMA inhibitors can be radio-labeled with diagnostic (68Ga-PSMA-11), or therapeutic nuclides (177Lu/225Ac PSMA-617) to be used as theranostic agent. Initial results showed that PSMA-targeted radioligand therapy can potentially delay disease progression in metastatic castrate-resistant PCa. This review aims to explore the current application of PSMA based imaging in prostate cancer, reporting about main advantages and limitations of this new theranostic procedure. The future perspectives and potential the applications of this agent will be also discussed.