Patterns of Failure Detected by PSMA PET After Primary, Salvage Radiotherapy for Prostate Cancer

A regional cohort analysis in Ontario, Canada, found that for patients with prostate cancer, prostate-specific membrane antigen positron emission tomography (PSMA PET) at baseline, before primary radiotherapy (pRT), or before salvage/adjuvant radiotherapy (sRT) may help identify which patients would benefit from pelvic radiotherapy and systemic therapy.

The analysis was presented at the 2023 American Society of Clinical Oncology Genitourinary Cancers Symposium.

For patients with prostate cancer and biochemical failure in Ontario, PSMA PET is available after definitive pRT or sRT through the province-wide PSMA-PET Registry for Recurrent Prostate Cancer (PREP).

Aruz Mesci, MD, FRCPC, and colleagues conducted a study to review patterns of PSMA-PET-detected failure after pRT or sRT in cohorts of PREP patients. The retrospective analysis included 104 pRT and 91 sRT patients who were imaged with ¹⁸F-DCFPyL PSMA PET from April 2019 to December 2021.

Median prostate-specific antigen before PSMA PET for the 2 groups was 5.0 ng/mL (interquartile range [IQR], 3.1-8.9) and 1.3 ng/mL (IQR, 0.6-3.4), respectively. The percentages of prostate or prostatic bed radiotherapy alone (Pr-RT) and Pr plus pelvic lymph node radiotherapy (Pr+LN-RT) treatments were 76% versus 24%, respectively, for the pRT group and 49.4% versus 50.6%, respectively, for the sRT group.

Researchers found that in the pRT group, increasing D’Amico risk category from low risk to high risk was associated with lower risk for local recurrence and increased risk for pelvic and distant metastasis. Additionally, pelvic radiotherapy was associated with a reduced risk for local recurrence in the pRT group but not in the sRT group.

“In this cohort of patients, PSMA PET detected a considerable risk for local recurrence in patients treated with pRT,” they concluded. “Studies with PSMA PET at baseline, before pRT or sRT, may help discern better [the] patients who would benefit from pelvic radiotherapy and systemic therapy.”