About

Matthias Benz is an Associate Professor in the Department of Pharmacology at the University of California, Los Angeles. His diagnostic clinical and research activities are centered on the use of advanced imaging modalities such as positron emission tomography (PET) and diffusion-weighted and dynamic contrast-enhanced magnetic resonance imaging (MRI) for the non-invasive diagnosis, staging, treatment response assessment, and follow-up of patients with cancer. He holds an M.D. degree and has a background that includes positions at the University Hospital Basel in Switzerland, where he served as an Assistant Professor of Radiology and Nuclear Medicine, as well as a resident in Nuclear Medicine and Radiology. Benz has also been a research fellow at UCLA's Ahmanson Translational Imaging Division and Nuclear Medicine. His academic career includes appointments as an Assistant Professor in the Departments of Radiological Sciences and Molecular and Medical Pharmacology at UCLA. His work integrates clinical imaging techniques with research to improve cancer diagnosis and management.

Research topics

• Medicine
• Internal medicine
• Nuclear medicine
• Oncology
• Radiology
• Biology
• Pathology

Selected publications

• [ ⁶⁸ Ga]Ga-FAPI-46 PET/CT in Adrenocortical Neoplasm, Oncocytic Type

  Journal of Nuclear Medicine · 2026-03-26

  article

  Adrenocortical neoplasm, oncocytic type (ACNO), known as adrenal oncocytoma, is a rare histologic subtype of adrenocortical neoplasms. Approximately one third of ACNOs are benign, 40% are borderline, and one fourth are malignant ([1][1]). Although benign and borderline ACNOs have a favorable

  PublisherDOI

• Clinical Context as a Clue to Interpreting PSMA-Avid Lesions on [18F]DCFPyL PET/CT in a Patient with Prostate Cancer and Clear Cell Renal Cell Carcinoma

  Nuclear Medicine and Molecular Imaging · 2026-03-21

  article
  PublisherDOI

• When PSMA lights up the thyroid: an incidental discovery of a second primary on [68Ga]Ga-PSMA-11

  European Journal of Nuclear Medicine and Molecular Imaging · 2025-06-05

  articleOpen access
  PublisherOA PDFDOI

• PSMA PET vs. pelvic MRI in biochemically recurrent prostate cancer.

  Journal of Clinical Oncology · 2025-02-10

  article

  40 Background: After primary definitive therapy of localized prostate cancer with either radical prostatectomy or radiation therapy, up to 50% of patients will experience biochemical recurrence (BCR) of disease. The objective of this descriptive, retrospective analysis is to compare the performance of PSMA PET/CT and pelvic MRI in BCR and investigate the added value of their combined use in this patient population. Methods: Patients with BCR who underwent PSMA PET/CT and pelvic MRI within three months of each other at the University of California, Los Angeles with available imaging and follow-up data were included in our retrospective analysis. Two board-certified nuclear medicine physicians blinded to clinical information interpreted the PSMA PET/CT scans independently and described up to three positive findings. A third nuclear medicine physician resolved any disagreements (2:1 majority rule). In a similar framework, two radiologists interpreted the pelvic MRIs with a third radiologist serving as a tiebreaker. For patients with metastatic disease, PSMA PET/CT scans were interpreted according to PROMISE criteria. Data on disagreements between clinical PSMA PET/CT and pelvic MRI reads, disagreements between blinded and clinical PSMA PET/CT and pelvic MRI reads, and subsequent management based on findings from clinical PSMA PET/CT and pelvic MRI were collected. Results: 101 patients were included in this retrospective analysis, of which 84 (83%) had localized BCR and 17 (17%) had metastatic BCR. 10/84 (12%) patients with localized BCR had a negative clinical pelvic MRI and positive PSMA PET/CT, with 33% of these lesions noted to be in the lymph nodes, while 8/84 (10%) patients had a negative clinical PSMA PET/CT and positive pelvic MRI, with 100% of these lesions noted to be in the prostate or prostate bed. 12/17 (71%) patients with metastatic BCR had a positive clinical PSMA PET/CT and negative pelvic MRI. In 10/84 (12%) patients with localized BCR, the blinded PSMA PET/CT reads were negative while the clinical PSMA PET/CT reads were positive, and in 7/84 (8%) patients, the blinded pelvic MRI reads were negative while the clinical pelvic MRI reads were positive. In 2/17 (12%) patients with metastatic BCR, the blinded PSMA PET/CT reads were negative while the clinical PSMA PET/CT reads were positive, and in 1/17 (6%) patients, the blinded pelvic MRI reads were negative while the clinical pelvic MRI reads were positive. 48% of patients underwent radiation as a next step in management, 26% underwent biopsy, 15% underwent follow-up imaging, and 11% underwent other focal or systemic therapy. Conclusions: In this retrospective, descriptive analysis, there was good agreement between PSMA PET/CT and pelvic MRI for localized BCR, although pelvic MRI may overcall lesions in the prostate and prostate bed and miss nodal metastases. For patients with metastatic BCR, PSMA PET can disclose lesions that are outside the field-of-view of pelvic MRI.

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• PSMA-PET/CT Findings in Patients With High-Risk Biochemically Recurrent Prostate Cancer With No Metastatic Disease by Conventional Imaging

  JAMA Network Open · 2025-01-03 · 54 citations

  articleOpen access

  Importance: The phase 3 randomized EMBARK trial evaluated enzalutamide with or without leuprolide in high-risk nonmetastatic hormone-sensitive prostate cancer. Eligibility relied on conventional imaging, which underdetects metastatic disease compared with prostate-specific membrane antigen-positron emission tomography (PSMA-PET). Objective: To describe the staging information obtained by PSMA-PET/computed tomography (PSMA-PET/CT) in a patient cohort eligible for the EMBARK trial. Design, Setting, and Participants: This post hoc, retrospective cross-sectional study included 182 patients from 4 prospective studies conducted from September 15, 2016, to September 27, 2021. All patients had recurrent prostate cancer after radical prostatectomy (RP), definitive radiotherapy (dRT), or salvage radiotherapy (SRT). Analysis was performed from January 2023 to July 2024. Exposures: Patients included had increasing prostate-specific antigen (PSA) levels greater than 1.0 ng/mL (after RP and SRT) or 2.0 ng/mL above the nadir value (after dRT), PSA doubling time of 9 months or less, and a serum testosterone level of 150 ng/dL or greater. Exclusion criteria were distant metastatic disease on radiographic imaging and prior hormonal or systemic therapy. Main Outcomes and Measures: Staging information obtained by PSMA-PET/CT in patients with nonmetastatic disease according to conventional imaging. Results: From 2002 patients screened, 182 (median age at PET/CT scan, 69 years [IQR, 64-73 years]) were included. Median prescan PSA levels were 2.4 ng/mL (IQR, 1.4-4.8 ng/mL) after RP (n = 91), 6.9 ng/mL (IQR, 3.5-18.5 ng/mL) after dRT (n = 39), 2.6 ng/mL (IQR, 1.6-5.2 ng/mL) after RP and SRT (n = 52), and 2.8 ng/mL (IQR, 1.7-6.6 ng/mL) overall (n = 182). Results of PSMA-PET were positive in 80% of patients (73 of 91) after RP, 92% of patients (36 of 39) after dRT, 85% of patients (44 of 52) after RP and SRT, and 84% of patients (153 of 182) overall. PSMA-PET detected any distant metastatic disease (miTxNxM1) in 34% of patients (31 of 91) after RP, 56% of patients (22 of 39) after dRT, 60% of patients (31 of 52) after RP and SRT, and 46% of patients (84 of 182) overall. Polymetastatic disease (≥5 lesions) was found in 19% of patients (17 of 91) after RP, 36% of patients (14 of 39) after dRT, 23% of patients (12 of 52) after RP and SRT, and 24% of patients (43 of 182) overall. Conclusions and Relevance: In a cohort of patients with high-risk hormone-sensitive prostate cancer without evidence of metastatic disease by conventional imaging, PSMA-PET results were positive in 84% of patients, detected M1 disease stage in 46% of patients, and found polymetastatic disease (≥5 lesions) in 24% of patients, suggesting that patients' high-risk nonmetastatic hormone-sensitive prostate cancers are understaged by conventional imaging. The results challenge the interpretation of previous studies, such as the EMBARK trial, and support the evolving role of PSMA-PET for patient selection in clinical and trial interventions in prostate cancer. Further studies are needed to assess its independent prognostic value and use for treatment guidance.

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• Clinical Impact of Changes in Tumor Uptake and Volume on PSMA PET/CT During [ ¹⁷⁷ Lu]Lu-PSMA Therapy in Metastatic Castration-Resistant Prostate Cancer

  Journal of Nuclear Medicine · 2025-10-30

  article

  Although tumor volume and new lesions (NLs) have been investigated previously as measures of response, the clinical impact of changes in tumor uptake on prostate-specific membrane antigen (PSMA) PET remains largely unknown. <b>Methods:</b> This multicenter retrospective study investigated the clinical impact of changes in tumor uptake and volume on PSMA PET during [¹⁷⁷Lu]Lu-PSMA in metastatic castration-resistant prostate cancer (mCRPC). The primary outcomes were the associations of changes in SUV_max (ΔSUV_max) and SUV_mean(ΔSUV_mean), changes in total tumor volume (ΔTTV), and occurrence of NLs with prostate-specific antigen (PSA) progression-free survival (PSA-PFS) and overall survival (OS). The study included patients with mCRPC who received [¹⁷⁷Lu]Lu-PSMA between 2014 and 2019. PSMA PET/CT was performed at baseline and after 2 cycles of therapy. Whole-body analyses (SUV_max, SUV_mean, TTV, and NLs) were performed and calculated using qPSMA software. <b>Results:</b> In total, 124 patients with mCRPC (median age, 73 y; interquartile range, 67–76 y) were included in the study. Whole-body ΔTTV and the occurrence of NLs were significantly associated with shorter PSA-PFS (hazard ratio [HR], 5.7; 95% CI, 3.59–9.06; and HR, 1.6; 95% CI, 1.4–1.8; <i>P</i> &lt; 0.0001) and with OS (HR, 2.3; 95% CI, 1.61–3.43; and HR, 1.3; 95% CI, 1.1–1.4; <i>P</i> &lt; 0.001). Patient-based analysis showed that ΔSUV_max and ΔSUV_mean were not associated with outcome (HR, 1.00; 95% CI, 0.99–1.00; <i>P</i> = 0.30; and HR, 0.90; 95% CI, 0.99–1.00; <i>P</i> = 0.11). Region-based analysis found that only ΔSUV_max in visceral lesions was significantly associated with PSA-PFS (<i>P</i> = 0.007) but not with OS. <b>Conclusion:</b> Only ΔTTV and the occurrence of NLs provided significant prognostic value and should be considered when evaluating treatment response to [¹⁷⁷Lu]Lu-PSMA therapy.

  PublisherDOI

• Low- and High-Volume Disease in Metastatic Hormone-Sensitive Prostate Cancer: From CHAARTED to PSMA PET—An International Multicenter Retrospective Study

  Journal of Nuclear Medicine · 2025-01-01 · 22 citations

  articleOpen access

  High-volume disease (HVD) and low-volume disease (LVD) definitions in metastatic hormone-sensitive prostate cancer (mHSPC) patients are based on conventional imaging (CI) (CT/MRI with bone scan [BS]) according to CHAARTED criteria. HVD and LVD definitions are associated with overall survival and are used for treatment decisions. It remains unknown how these definitions transfer to prostate-specific membrane antigen (PSMA) PET imaging. The aim of this retrospective multicenter study was to compare the CI-based disease volume criteria to PSMA PET–based volume definitions in a CHAARTED-like cohort. <b>Methods:</b> mHSPC patients from 5 international sites who underwent PSMA PET/CT or PSMA PET/MRI and BS within a time interval of 100 d and without initiation of a new therapy between the 2 scans were retrospectively included in the analysis. CHAARTED HVD and LVD criteria were applied to BS, CT, MRI, and PSMA PET. HVD was defined by the presence of visceral metastases or at least 4 bone metastases (with ≥1 beyond the spine or pelvis). Whole-body (WB) tumor burden was estimated with the automated bone scan index (aBSI, EXINI v2.0) on BS and with the WB PSMA PET–positive tumor volume (PSMA-TV) on PSMA PET, respectively. <b>Results:</b> Sixty-seven patients with paired PSMA PET and BS were included. The median prostate-specific antigen level was 54.9 ng/mL (interquartile range [IQR], 10.4–191.0 ng/mL). On the basis of CI, it was determined that 17 of 67 patients had HVD-CI (25.4%) and 50 of 67 patients had LVD-CI (74.6%). On the basis of PSMA PET, it was determined that 27 of 67 patients had HVD-PET (40.3%) and 24 of 67 patients had LVD-PET (35.8%). In total, 16 of 67 patients (22.4%) had no visible lesion or only locoregional pelvic disease (M0) with PSMA PET (M0-PET). Stage migration between CI and PSMA PET occurred in 27 of 67 patients (40.3%) by both upstaging and downstaging: 11 of 50 (22%) LVD-CI patients were HVD-PET, whereas 1 of 17 (5.9%) HVD-CI and 15 of 50 (30%) of LVD-CI patients were M0-PET. The median WB PSMA-TV and automated BS index were 248.0 mL (IQR, 54.6–1,427.0 mL) and 3.4% (IQR, 1,0–7.2%) for HVD-CI, 25.1 mL (IQR, 6.6–74.6 mL) and 0.1% (IQR, 0.0–0.2%) for LVD-CI, 141.0 mL (IQR, 47.5–458.0 mL) and 0.9% (IQR, 0.04–4.1%) for HVD-PET, and 31.5 mL (IQR, 10.1–67.9 mL) and 0% (IQR, 0–0.1%) for LVD-PET, respectively. The optimal WB PSMA-TV to stratify CI-based CHAARTED LVD-CI versus HVD-CI was 107 mL with a misclassification of 21.9%. <b>Conclusion:</b> Compared with CI, addition of PSMA PET leads to M0 downstaging in every third and LVD to HVD upstaging in every fifth mHSPC patient. Future HVD and LVD definitions based on PSMA PET/CT should be adjusted based on patient outcome.

  PublisherOA PDFDOI

• RECIP 1.0 Predicts Progression-Free Survival After [¹⁷⁷Lu]Lu-PSMA Radiopharmaceutical Therapy in Patients with Metastatic Castration-Resistant Prostate Cancer

  Journal of Nuclear Medicine · 2024-04-18 · 22 citations

  articleOpen access

  Response Evaluation Criteria in Prostate-Specific Membrane Antigen Imaging (RECIP) 1.0 is an evidence-based framework to evaluate therapeutic efficacy in metastatic prostate cancer using prostate-specific membrane antigen (PSMA) PET/CT. This study aimed to evaluate the associations of interim PSMA PET/CT by RECIP 1.0 with short-term outcome after radiopharmaceutical treatment. <b>Methods:</b> This multicenter retrospective study included patients with metastatic castration-resistant prostate cancer who underwent [¹⁷⁷Lu]Lu-PSMA radiopharmaceutical therapy at 3 academic centers and received PSMA PET/CT at baseline and at 12 wk. Pairs of PSMA PET/CT images were assessed by 5 readers for visual RECIP 1.0. The primary outcome was the association of RECIP with prostate-specific antigen progression-free survival (PSA-PFS) by Kaplan–Meier analysis. <b>Results:</b> In total, 124 of 287 screened patients met the inclusion criteria, with 0 (0%), 29 (23%), 54 (44%), and 41 (33%) of those 124 patients having complete response, partial response, stable disease, or progressive disease (PD) by visual RECIP 1.0, respectively. Patients with visual RECIP PD had a significantly shorter PSA-PFS than those with RECIP stable disease or with RECIP partial response (2.6 vs. 6.4 vs. 8.4 mo; <i>P</i> &lt; 0.001). The median PSA-PFS among patients with RECIP PD versus those with non-RECIP PD was 2.6 versus 7.2 mo (hazard ratio, 13.0; 95% CI, 7.0–24.1; <i>P</i> &lt; 0.001). <b>Conclusion:</b> PSMA PET/CT by RECIP 1.0 after 2 cycles of [¹⁷⁷Lu]Lu-PSMA is prognostic for PSA-PFS. PSMA PET/CT by RECIP 1.0 may be used in earlier stages of prostate cancer to evaluate drug efficacy and to predict progression-free survival.

  PublisherOA PDFDOI

• Response evaluation criteria in PSMA PET/CT (RECIP 1.0) in metastatic castration-resistant prostate cancer.

  Journal of Clinical Oncology · 2024-01-29

  article

  45 Background: Response Evaluation Criteria in Prostate-Specific Membrane Antigen (PSMA) PET/CT (RECIP 1.0) initially integrated software-based quantitative assessment of PSMA-positive total tumor volume (PSMA-VOL). Clinical implementation of such software is not expected soon, limiting the use of RECIP in practice. This study aimed to assess the agreement of RECIP determined using tumor segmentation software (quantitative RECIP) with RECIP determined by qualitative reads by nuclear medicine physicians (visual RECIP) for response evaluation in metastatic castration-resistant prostate cancer. Methods: This multicenter retrospective study at three academic centers included patients who received lutetium-177 ( 177 Lu) PSMA treatment between December 2014 and July 2019. PSMA PET/CT images at baseline and 12 weeks were assessed qualitatively by five nuclear medicine physicians for changes in PSMA-VOL and for new lesions. Quantitative changes in PSMA-VOL were also measured using tumor segmentation software. The status of new lesions was combined with qualitative changes in PSMA-VOL to determine visual RECIP and with quantitative changes in PSMA-VOL to determine quantitative RECIP. The primary outcomes were the agreement between visual and quantitative RECIP and the interreader reliability of visual RECIP according to the Fleiss κ. The secondary outcome was the association of visual RECIP with overall survival according to Cox regression. Results: A total of 124 patients (median age, 73 years [IQR, 67–76 years]) were included. Forty (32%) and 84 (68%) patients had quantitative RECIP progressive disease (PD) and non-PD, respectively. Agreement between visual versus quantitative RECIP was excellent (κ=0.89; 118 of 124 patients [95%]). Agreement among readers in classifying visual RECIP PD versus non-PD was excellent (κ=0.81; 103 of 124 patients [83%]). RECIP-PD was associated with significantly shorter overall survival compared with RECIP-nonPD (hazard ratio, 2.6 [95%CI: 1.7, 3.8]; P &lt;.001). Conclusions: Qualitatively assessed RECIP demonstrated excellent agreement with quantitative RECIP and excellent interreader reliability, and can be readily implemented in clinical practice for response evaluation in patients with metastatic castration-resistant prostate cancer undergoing 177 Lu-PSMA therapy and possible other systemic therapies.

  PublisherDOI

• A call for objectivity: Radiologists’ proposed wishlist for response evaluation in solid tumors (RECIST 1.1)

  Cancer Imaging · 2024-11-14 · 6 citations

  reviewOpen access

  The Response Evaluation in Solid Tumors (RECIST) 1.1 provides key guidance for performing imaging response assessment and defines image-based outcome metrics in oncology clinical trials, including progression free survival. In this framework, tumors identified on imaging are designated as either target lesions, non-target disease or new lesions and a structured categorical response is assigned at each imaging time point. While RECIST provides definitions for these categories, it specifically and objectively defines only the target disease. Predefined thresholds of size change provide unbiased metrics for determining objective response and disease progression of the target lesions. However, worsening of non-target disease or emergence of new lesions is given the same importance in determining disease progression despite these being qualitatively assessed and less rigorously defined. The subjective assessment of non-target and new disease contributes to reader variability, which can impact the quality of image interpretation and even the determination of progression free survival. The RECIST Working Group has made significant efforts in developing RECIST 1.1 beyond its initial publication, particularly in its application to targeted agents and immunotherapy. A review of the literature highlights that the Working Group has occasionally employed or adopted objective measures for assessing non-target and new lesions in their evaluation of RECIST-based outcome measures. Perhaps a prospective evaluation of these more objective definitions for non-target and new lesions within the framework of RECIST 1.1 might improve reader interpretation. Ideally, these changes could also better align with clinically meaningful outcome measures of patient survival or quality of life.

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Frequent coauthors

• William D. Tap

  81 shared

• Fritz C. Eilber

  University of California, Los Angeles

  80 shared

• Daniel Braas

  69 shared

• Ethan Ahler

  69 shared

• Kathleen B. Smith

  69 shared

• Brenna Tam

  69 shared

• Mirielle Riedinger

  69 shared

• David A. Nathanson

  67 shared