PET Radiotracer Boosts Survival in Postprostatectomy Salvage Radiotherapy

Patients who underwent advanced molecular imaging had higher rates of disease-free survival, according to new research.

A new report shows advanced molecular imaging techniques can improve long-term survival in patients with prostate cancer who undergo prostatectomies.

The study published in The Lancet concerns the PET radiotracer 18F-fluciclovine (18F; Axumin), a synthetic amino acid first developed at Emory University’s Center for Systems Imaging and later approved by the FDA for imaging of prostate cancer recurrence. Co-author Ashesh B. Jani, MD, of Emory’s Winship Cancer Institute, said imaging plays an important role in guiding decision-making in radiotherapy following surgery.

“The decision to offer post-prostatectomy radiation is complex, because conventional imaging can leave unanswered questions on the best approach for treatment planning,” Jani said in a press release.

Previous studies have found that as many as 20% to 60% of patients with prostate cancer experience inadequate response to treatment or disease progression following surgery. Whether to proceed with radiotherapy is a decision typically made based on factors such as individual risk, pathological findings, and prostate-specific antigen (PSA) trajectory. Conventional imaging, such as CT scans, is often used but has a low diagnostic yield, Jani and colleagues explained, particularly at PSA concentrations below 2 ng/mL. MRI, they said, can be useful in some circumstances, but also has significant limitations.

Jani and colleagues wondered if molecular imaging with 18F PET/CT would lead to more accurate characterizations of patient cases, and therefore to better decision making with regard to adjuvant radiotherapy. To test the hypothesis, the investigators enrolled 165 patients who experienced recurrence following prostatectomy into an open-label, randomized controlled phase 2/3 trial. The patients all had detectable PSA but no extrapelvic or bone findings using conventional imaging. Half of the patients were given radiotherapy using conventional imaging methods, while the other group’s radiotherapy was guided using 18F PET/CT imaging. The primary end point was 3-year event-free survival. “Events” were defined as biochemical or clinical recurrence or progression or the initiation of systemic therapy.

After 3 years, the investigators found 75.5% of patients in the 18F group were disease free versus 63% of patients in the conventional imaging group.

“This research has found that integrating advanced PET imaging using fluciclovine allows us to do a better job of selecting patients for radiation therapy, guiding radiation decisions and planning, and ultimately, keeping our patients’ cancer under control,” Jani said.

The study included patients enrolled between 2012 and 2019. At the beginning of the enrollment period, Jani and colleagues noted, molecular imaging had not yet become a routine part of prostate cancer care. Previous studies have shown the technique can improve imaging, but until now there has not yet been a rigorous trial evaluating the impact of PET radiotracers in a postprostatectomy setting.

The authors noted some limitations to their study, including the fact that it took place over a 7-year period, during which treatment norms had evolved. Also, while post-PET decisions were rigidly determined by PET findings, there were variations in pre-PET decisions.

Overall, though, the authors said the data show molecular imaging can have an important impact on patient outcomes.

Jani and colleagues plan to continue investigating newer types of imaging, including prostate-specific membrane antigen (PSMA) PET, a radiotracer targeting a receptor on the surface of prostate cancer cells. They want to know whether the new imaging technique might further improve cancer control in patients with prostate cancer.

Reference

Jani AB, Schreibmann E, Goyal S, et al. 18F-fluciclovine-PET/CT imaging versus conventional imaging alone to guide postprostatectomy salvage radiotherapy for prostate cancer (EMPIRE-1): a single centre, open-label, phase 2/3 randomised controlled trial. Lancet. 2021;397(10288):1895-1904. doi:10.1016/S0140-6736(21)00581-X