Hiding in plain sight.

Top Line: How does pre-treatment PSMA PET/CT impact curative-intent prostate radiation?

The Study: PSMAgRT was a randomized phase II trial of 253 patients eligible for curative intent radiation who fell into one of four categories based on conventional imaging: high risk intact (CAPRA score ≥6 or N1), post-operative salvage, post-radiation salvage (confirmed local recurrence), and oligometastatic (≤5 mets with ≤3 non-bone mets amenable to SBRT). This study reports on secondary outcomes from the trial with the primary failure-free survival outcome pending. Most patients were in the salvage post-prostatectomy category (50.6%) followed by high risk intact (34%), oligometastatic (9.1%), and post-RT (6.3%). They were randomized to have PSMA PET and then PET-directed, intensified RT. Overall, nearly half of patients had new, previously unknown lesions detected by PSMA PET. This included a whopping 51.6% of post-op patients, 45.5% of oligometastatic patients, 39.5% of high risk patients, and 14.3% of post-RT patients. In fact, these 56 patients had 170 new lesions. The most frequent site of new lesions was pelvic lymph nodes (55.1%) followed by the prostate fossa (23.2%), bone (14.5%), prostate (2.9%), seminal vesicles (2.9%), and para-aortic nodes (1.4%). Another important factor in detecting new lesions was PSA level. A third of patients with a PSA of 0.1-0.2 had new lesions compared to 52.4% when the PSA was 0.2-0.3 and 75% when it was 0.3-0.4. So, how did these findings affect treatment? Over half of patients randomized to pre-treatment PSMA had a change in treatment strategy with the most common being a lymph node boost in 25%. The true test from this and other trials will be whether PET-directed treatment intensification improves survival outcomes. Fluciclovine PET before salvage RT improved event free survival in the EMPIRE-1 trial, so our hopes are high for PSMA.

TBL: Across a broad spectrum of patients receiving curative radiation for prostate cancer, pre-treatment PSMA identified new lesions and changed treatment in over half of patients. | Petit, Int J Radiat Oncol Biol Phys 2023