(UroToday.com) The 2025 GU ASCO annual meeting featured a prostate cancer session and a presentation by Dr. Melissa Abel discussing radium-223 without androgen deprivation therapy (ADT) in patients with biochemically recurrent prostate cancer and PET findings in the bones. Biochemically recurrent prostate cancer patients have a rising PSA after definitive surgery or radiation, but negative CT/99Tc scans. While ADT-based strategies are commonly used, they can be associated with life-altering toxicities and have not been shown to improve survival.
Radium-223 is an alpha-emitting radiopharmaceutical that accumulates in areas of high bone turnover and has demonstrated a survival benefit in metastatic prostate cancer,1 but its benefits as a monotherapy in biochemically recurrent prostate cancer without ADT have not been explored prior to this study. This strategy may be important as bone metastasis drives morbidity and mortality in prostate cancer.
Eligible patients in this study had biochemically recurrent prostate cancer following definitive therapy, testosterone >100ng/dL, normal organ and marrow function, and negative CT/99Tc imaging. Patients must have positive findings on a NaF or PSMA PET suspicious for metastatic bone disease not seen on 99Tc. Patients were treated with radium-223 at the approved dosing of 55 kBq/kg for 6 cycles. PSA declines were defined as 2 or more confirmed declines from an intra-study apex PSA. All patients had pre- and post-treatment PSMA and NaF imaging, and immune responses (primary endpoint) are to be evaluated at study completion.
To date, 18 patients have enrolled with 16 currently evaluable for response, with a median age of 67 years (range: 58-80) and median PSA of 1.75 ng/ml (range: 0.2-49.5); 14 of 16 patients had PSMA positive scans and 13 of 16 patients had NaF positive scans. There have been no missed cycles for toxicity and no grade >3 toxicities. Grade 2 toxicities have been rare and no Grade 1 or 2 changes in hemoglobin or platelets have occurred. Two patients with rapid PSA doubling times came off for progression and were not evaluable for follow up imaging. Five patients (31%) had confirmed intra-study apex PSA declines of 14%, 21%, 24%, 33%, and 57% lasting 84, 173, 292, 246+, and 661+ days, respectively. There were 8 of 11 evaluable patients that had evidence of decreased SUV on NaF PET imaging after treatment. Two patients had resolution of multiple PSMA positive bone findings, and one patient remains with negative bone findings on PET after 2+ years and with a stable PSA.
Dr. Abel concluded her presentation discussing radium-223 without ADT in patients with biochemically recurrent prostate cancer and PET findings in the bones with the following take-home points:
- Radium-223 in biochemically recurrent prostate cancer is safe and associated with rare grade 1/2 toxicities
- Decreases in SUV seen on most NaF scans suggest radium-223 targeting of suspicious lesions
- Substantial improvements in PSMA imaging have been observed
- Delayed but confirmed PSA declines have been seen in 31% of patients
- Radium-223 monotherapy may have a therapeutic activity in biochemically recurrent prostate cancer and further studies are needed to define its potential role in PET positive biochemically recurrent prostate cancer
Presented by: Melissa L. Abel, MD, National Institutes of Health, Bethesda, MD
Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Associate Professor of Urology, Georgia Cancer Center, Wellstar MCG Health, @zklaassen_md on Twitter during the 2025 Genitourinary (GU) American Society of Clinical Oncology (ASCO) Annual Meeting, San Francisco, CA, Thurs, Feb 13 – Sat, Feb 15, 2025.
Reference:
- Parker C, Nilsson S, Heinrich D, et al. Alpha emitter radium-223 and survival in metastatic prostate cancer. N Engl J Med 2013;369(3):213-223.