ASCO 2023: Early Changes of PSMA PET Signal After Initiation of Androgen Receptor Signaling Inhibitors in mCRPC: An International Multicenter Retrospective Study

(UroToday.com) The 2023 American Society of Clinical Oncology (ASCO) annual meeting held in Chicago, IL between June 2nd and June 6th was host to a prostate, testicular, and penile cancers poster session. Dr. Lena Unterrainer presented the results of an international multicenter retrospective study evaluating early changes in PSMA-PET/CT signaling following initiation of androgen receptor signaling inhibitors (ARSIs) in mCRPC patients.


Since the initial reports of prostate-specific membrane antigen (PSMA)-based PET/CT for prostate cancer emerged in 2013, the use of PSMA-based imaging has seen significant growth. Currently, 68Ga-PSMA-11 and 18F-DCFPyL-PET/CT are both FDA approved for the initial staging of high-risk patients prior to definitive therapy and for those with biochemical recurrence. There is emerging evidence that exposure to systemic hormonal therapy may affect PSMA expression levels, inducing a “PSMA flare”, and thus altering PSMA-PET/CT findings . The objective of this study was to evaluate early changes of PSMA expression by PET in mCRPC patients.

This was a retrospective study across five international sites of mCRPC patients undergoing a 68Ga-PSMA-11 PET/CT both prior to (PET1) and early after ARSI use (PET2 within a maximum of 29 days). Whole-body PSMA-positive tumor volume (PSMA-TV) was evaluated using a liver-specific semi-automatically threshold (Affinity 3.0.2, Hermes Medical Solutions). Whole-body PSMA-TV, SUVmean and SUVmax and their respective changes (%) were analyzed. PSA changes between PET 1 and PET2 were similarly evaluated.

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This analysis included a total of 54 patients. ARSI was initiated at a median of 1 day (range: 0 – 28) after PET1, while PET2 was performed at a median of 14 days (range 7 – 29) post-ARSI initiation. The median serum PSA level decreased from 9.5 ng/ml at PET1 to 8.7 ng/ml at PET2 (p=0.035). The whole body PSMA-TV increased from 89.9 ml at PET1 to 112.2 ml at PET2 (p=0.016). There were no significant differences in in whole body PSMA SUVmean (9.0 and 9.3, respectively, p=0.19) or SUVmax (26.5 versus 28.5, p=0.35).

Four of 7 patients with PSA increases at PET2 had an increasing PSMA-TV, 6/7 showed an increasing SUVmean and 5/7 presented with an increased SUVmax. Decreasing whole body PSMA-TV in 18/54 (33%) patients was accompanied by decreasing SUVs in 10 of them (56%). Percent PSA change was unrelated to changes in PSMA-TV, SUVmean and SUVmax.

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In summary, PSMA-PET/CT performed early after ARSI initiation was associated with slight increases in whole-body PSMA-TV, but no significant changes in whole body PSMA SUVmean or SUVmax. The authors concluded that ARSI use does not have a strong effect on PSMA expression within 30 days of treatment initiation.

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Presented by: Lena Unterrainer, MD, Ahmanson Translational Theranostics Division, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, UCLA, Los Angeles, CA

Written by: Rashid Sayyid, MD, MSc – Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the 2023 American Society of Clinical Oncology (ASCO) Annual Meeting, Chicago, IL, Fri, June 2 – Tues, June 6, 2023.